212 Sentences With "nacreous" | Random Sentence Generator

In a new study, three scientists claim that Edvard Munch's iconic image was inspired by nacreous clouds, a rare meteorological phenomenon.

Depending on the lighting (beautifully manipulated by Nicholas Houfek), they could look monolithic or flimsy, with the nacreous shimmer of spilled oil.

"The position of the vortex shifts towards the end of the week taking the coldest air, and the Nacreous Clouds, away from above the UK."

Photographer Ceri Oakes took to Twitter on Tuesday morning to share a photo of some nacreous clouds taken in North Yorkshire, UK — but the picture ended up capturing people's attention for different reasons.

Where the previous photo paintings relied mostly on a gray-scale palette, Ema glows with nacreous pink skin and golden hair—her body "seems to shine from within," as one critic put it.

LONDON — If you happen to have looked up into the sky recently and spotted strange patterns of shifting colours, don't panic — the weird bodies of lights appearing above Britain aren't UFOs, they're nacreous clouds.

In a research paper presented this week at the general assembly of the European Geosciences Union in Vienna, three meteorologists argue that Munch's wavy red, yellow, and blue skies are in fact a representation of a rare nacreous or "mother-of-pearl" cloud formation.

The umbilical depression is excavated, nacreous, iridescent, and surrounded by slight concentric grooves. The semioval aperture is nacreous within. The columellar margin is recurved with a nacreous callosity. The nearly sharp outer lip is not reflexed.

The height of the translucent nacreous, white shell attains 3 mm.

The height of this translucent, nacreous, white shell attains 3.7 mm.

The height of this translucent, nacreous, white shell attains 3.5 mm.

The height of this translucent, nacreous, white shell attains 3.1 mm.

The white, nacreous shell is broader (3.9 mm) than high (3.8 mm).

The translucent nacreous, white shell is broader (6.8 mm) than high (6.4 mm).

The body whorl is less contracted behind the lip, which is not produced forward above. The umbilical callus is not nacreous. It has a granular surface, white and covering less than half the umbilicus. The lip and the aperture oare only slightly nacreous.

They may either have metallic, matted, or nacreous scales. Telescope eyes can grow quite large.

The lirae are coarsely granulose, about 5 in number. The aperture is very oblique. The outer lip is edged with blackish, then nacreous, and lined with opaque white, the thickening slightly notched at the place of the periphery. The oblique columella is nearly straight, flat, opaque white and backed by nacreous.

However, the inner layer in the great majority of mollusc shells is porcellaneous, not nacreous, and this usually results in a non-iridescent shine, or more rarely in non-nacreous iridescence such as flame structure as is found in conch pearls. The outer layer of cultured pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Other mollusc families that have a nacreous inner shell layer include marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.

The white, depressed shell is wider (7.30 mm) than high (3.35 mm). It is thin, highly polished and translucent nacreous.

The white, thin, umbilicate, and depressed shell is markedly broader (8.35 mm) than high (5.65 mm). It is translucent nacreous.

This type of PSC is also referred to as nacreous (, from nacre, or mother of pearl, due to its iridescence).

The nacreous, white shell is somewhat broader (2.45 mm) than high (2.1 mm). The thick shell has a narrow umbilicus.

The nacreous layer of monoplacophoran shells appears to have undergone some modification. Whilst normal nacre, and indeed part of the nacreous layer of one monoplacophoran species (Veleropilina zografi), consists of "brick-like" crystals of aragonite, in monoplacophora these bricks are more like layered sheets. The c-axis is perpendicular to the shell wall, and the a-axis parallel to the growth direction. This foliated aragonite is presumed to have evolved from the nacreous layer, with which it has historically been confused, but represents a novelty within the molluscs.

Fragum fragum grows to a length of . It has a pair of white, thick, sculptured valves with a nacreous coating on the interior.

Its upper margin is slightly curved, but less so than the basal one. The columellar margin is nearly straight, joining the basal margin with an angle, at the end of the umbilical angle, slightly crenulated by the umbilical lirae. The margins are connected by a thin nacreous layer. The interior of the aperture is nacreous, smooth, and slightly thickened near the margins.

The columellar margin is flattened. The regularly oval aperture is nacreous and striate within. The operculum is very thin.G.W. Tryon (1890), Manual of Conchology vol.

The thin, translucent, white shell has a trochiform shape. They are small or very small. Their maximum height is 22 mm. They are usually nacreous.

The aperture is rounded-subquadrate. Its right margin is incomplete, its columellar margin is curved, with a denticle in the basal part. It is slightly reflected over the umbilicus. The interior of the shell is nacreous, (the nacreous texture of the inner layers is clearly visible on some of the exterior parts, where the outer layer has been removed by accidents during the youth of the animal).

Polar stratospheric clouds form at very high altitudes in polar regions of the stratosphere. Those that show mother-of-pearl colors are given the name nacreous.

The edges are simple, not thickened. The thin operculum is corneous and multispiral. The shell is nacreous, with delicate suffused splashes of brown.Dall, W. H. 1881.

The height of the thin, white shell attains 2.3 mm. It is strongly depressed with a width of 6.85 mm. It is umbilicate and translucent nacreous.

Lustrin A is an insoluble protein used in the production of a nacreous layer in bivalve molluscs. It contributes to the properties of the nacreous layer, imparting resistance to cracking and elasticity. This is accomplished by its structure; it consists of many spring-like units which can expand when the shell is under extensional pressure. Its structure is similar to that of proteins involved in silica deposition in diatoms.

The height of the white shell attains 0.28 mm, its diameter 0.82 mm. The minute shell has a discoid shape. It is not nacreous. The spire is sunken.

The low spire is rather short. The acute apex is red or purplish. The oblique, rhomboidal aperture is white and nacreous. The lip is very much thickened within.

The solid, cancellated shell has a subdiscoidal shape. Its umbilicus is large, with a spiral funiculum. The aperture is not nacreous. The peristome is varicose, reflected and sub-bilabiate.

The operculum is pale brown with about eight turns. The aperture is rounded and slightly angular above. The outer lip simple and sharp. The body shows a thin nacreous glaze.

The thin shell has a turbinate or subtrochoid shape. It is translucent, the outer layer very slight, somewhat nacreous in fresh specimens. There is no epidermis. The shell contains spiral carinations.

The rounded aperture is slightly angular above. The outer lip is simple and sharp. The body has a thin nacreous glaze. The columellar lip is rounded, and broader than the rest.

These bivalves are distinguished by the presence of relatively primitive, "protobranchiate" gills. There are a row of short teeth along the hinge of the shell. The shells are often internally nacreous.

PDF (Original description W.H. Dall) Shell in general features recalling Gaza daedala, much of whose description would apply with little change to this species. The eight whorls are in the adult roundly shouldered below the suture, rounded at the periphery, somewhat flattened on the base, and deeply and widely umbilicated. The umbilicus is a little more than half covered by a nacreous callus. The first 2½ whorls are transparent, not nacreous, very obtuse with the nucleus not prominent.

The minute apex is recumbent, spiral, and dextral. The tip is eroded. The inside is scarcely nacreous, the color pattern showing through. This is a shell smaller than Broderipia iridescens, and more convex.

Supercooled nitric acid and water PSC's, sometimes known as type 1, typically have a stratiform appearance resembling cirrostratus or haze, but because they are not frozen into crystals, do not show the pastel colours of the nacreous types. This type of PSC has been identified as a cause of ozone depletion in the stratosphere. The frozen nacreous types are typically very thin with mother-of-pearl colorations and an undulating cirriform or lenticular (stratocumuliform) appearance. These are sometimes known as type 2.

Lenticular nacreous clouds over Antarctica Polar stratospheric clouds (PSC's) form in the lowest part of the stratosphere during the winter, at the altitude and during the season that produces the coldest temperatures and therefore the best chances of triggering condensation caused by adiabatic cooling. Moisture is scarce in the stratosphere, so nacreous and non-nacreous cloud at this altitude range is restricted to polar regions in the winter where the air is coldest. PSC's show some variation in structure according to their chemical makeup and atmospheric conditions, but are limited to a single very high range of altitude of about , so they are not classified into altitude levels, genus types, species, or varieties. There is no Latin nomenclature in the manner of tropospheric clouds, but rather descriptive names using common English.

The apex is often worn away in adults. The columella has a prominent, blunt tooth. The inner edge of the outer lip shows a number of smaller knobs. The aperture has a nacreous interior.

The height of the shell attains 23.2 mm., its diameter 26.9 mm. The nacreous white shell is rather large for the genus and contains 3½ rapidly enlarging whorls. The whorls have a smooth surface.

The body whorl is strongly angled or carinate at the periphery. The base of the shell is plano-concave. The suture is rather deep. The aperture is suboval to quadrangular and is nacreous within.

The size of the shell varies between 2.7 mm and 4.4 mm. The shell thin, transparent, glossy, but not nacreous forms a depressed cone. Its color is glassy. The shell is umbilicated and rather smooth.

The size of the shell varies between 4 mm and 9 mm. The imperforate, rather thin shell has a conical shape. It is olivaceous with nacreous reflections. It is ornamented with flexuous longitudinal grayish streaks.

The shell is smooth or with about 12 smooth spiral ridges. The broad umbilicus is funnel-shaped. The nacreous aperture is oval with the long axis inclined to the left. It is also prosocline, i.e.

Their height may vary between 3 mm and 152 mm. The shell contains only a few whorls. These have a highly variable exterior, ranging from smooth or glossy to sculptured. The internal shell is nacreous.

The length of the shell reaches 11 mm. The shell has a depressedly conoidal shape. It is sharply keeled, with a flat base and large umbilicus. It is nacreous under a thin, transparent, yellowish-white layer.

The aperture (opening) is nacreous (pearly). The base is almost flat and is sculpted with numerous minutely granulated spiral cords. The color is yellowish brown with reddish brown maculations.Shells of the Western Pacific in Color, Vol.

The umbilicus and its margin are pure white, the aperture nacreous green.Verco, J.C. 1904. Notes on South Australian marine Mollusca with descriptions of New Species. Part I.; Transactions of the Royal Society of South Australia v.

The white semicircular aperture has a nacreous gloss. The thick outer lip has no inner lirae. The columella shows two folds with a conspicuous tooth close to the siphonal canal. The umbilicus is closed by a callus.

Gills range from protobranch to eulamellibranch. Teleodesmacea on the other hand have a porcelanous and partly nacreous shell structure; Mantle lobes that are generally connected, well developed siphons, and specialized hinge teeth. In most, gills are eulamellibranch.

Having the sexes united in the same individual. Multifid. Made up of many lobes or projections, as the cusps on some radulae. Multispiral. Consisting of many whorls, as some fresh-water snails. Nacreous. Pearly or iridescent. Nepionic.

This number is not fixed and can vary within a species and between populations. Abalones have no operculum. The aperture of the shell is very wide and nacreous. The exterior of the shell is striated and dull.

The nodes on the upper carina become little raised hollow rounded squamae on the second whorl. The aperture has a reflexed and thickened margin. The umbilicus is very wide and spirally dentate. This shell is nacreous within.

The base of the shell is coarsely lirate, lirae about 9 in number. The aperture is small, quadrangular, and smooth within. The lip is acute, bordered inside by a wide porcellanous band. The throat is nacreous, brilliant green.

Sculpture gradually disappearing and becoming smooth towards body whorl excepting irregular growth lines, but remaining faintly at base. Sutural ramp moderately rugose. Umbilicus circular, narrow and deep. Nacreous part of parietal wall widely extended beyond umbilicus by secondary resorption.

All have in common a larval stage that is temporarily parasitic on fish, nacreous shells, high in organic matter, that may crack upon drying out, and siphons too short to permit the animal to live deeply buried in sediment.

Shells of the Anomphalidae are rounded, almost discoidal, low-spired trochospiral inform, possibly with a globular body whorl. The aperture is oval, without exhalent slit or crease. The umbilicus is narrow, open or closed. The inner shell layer is seemingly nacreous.

The height of the shell attains 2.5 mm, its diameter 4 mm. The rather small, nacreous shell is wider than high. The surface appears perfectly smooth and glazed with traces of brown wavy lines. The depressed spire has a conoidal shape.

The periostracum and prismatic layer are secreted by a marginal band of cells, so that the shell grows at its outer edge. Conversely, the nacreous layer is derived from the main surface of the mantle."integument (mollusks)."Encyclopædia Britannica. 2009.

The species in this genus are small to minute. They have a depressed or turbinate shape. They are all umbilicated with a nacreous inner layer. The thickened outer lip, attached to the body whorl for a short length, is continuous.

The height of the shell attains 7 mm, its diameter 7½ mm. The rather thin shell is narrowly perforated and has a trochiform shape. The white surface is very shining with nacreous reflections. The conic spire occupies half of the length.

The body whorl is wide, furnished with another angle on the base. The base is convex, and multi-lirate. The umbilicus is closed and is a bone to ivory color, and the interior is brightly nacreous. The aperture is rhomboid- orbicular.

The aperture is subcircular, slightly angular above and compressed near the periphery. The outer margin is thin. The columellar margin is sinuous, thickened, slightly reflected above, running without appreciable angle into the basal margin. The interior of the aperture is nacreous.

The shell contains about 5 convex whorls, the last very rapidly widening, somewhat descending toward the aperture. The rounded aperture is oblique, angular above, nacreous inside. The pearly iridescence is often visible through the shell. The narrow umbilicus is profound.

Each species has a typical number of open holes, between four and 10, in the selenizone. An abalone has no operculum. The aperture of the shell is very wide and nacreous. The exterior of the shell is striated and dull.

Along the coast of Brazil, they are known to spawn once in the winter and once again in the summer. Lion's paws rarely produce pearls, however, when they do, the pearl is composed mainly of calcite and are non-nacreous.

A orange fancy fantail goldfish. The Fantail goldfish may have either metallic or nacreous scales and normal or telescope eyes. Telescope eyes do not develop until the fish is 6 months old. Its fins are less developed than the Ryukin.

Some of the regulatory proteins in mineralized tissues are osteonectin, osteopontin, osteocalcin, bone sialoprotein and dentin phosphophoryn. In nacre, the organic component is porous, which allows the formation of mineral bridges responsible for the growth and order of the nacreous tablets.

The background color of the first whorls is typically reddish, the later whorls usually whitish with red, brown or (more rarely) black flames. The peripheral cord is usually articulated with red and white. The apex is pink. Interior of aperture is nacreous.

These are nearly flat, the last one is obtusely angled at the periphery. The base of the shell is rather flattened. The rounded aperture is quadrangular, very similar in shape to that of Calliostoma punctulatum. It is nacreous, iridescent and sulcate within.

The basal lip is thickened, subdentate, uniting with the columella in a regular curve. The columella is oblique, with a deep fold near its insertion, and is smooth within. The umbilical area contains 3 to 4 spiral ribs. The interstices are nacreous.

The shell in this genus is like the shell of Diloma but rather more conical and less nacreous. The coloration is variegated, consisting of fine lines of dark on a lighter ground. The columella is generally green. The umbilicus is perforate or subperforate.

The aperture is nearly circular. The thin outer and basal margin are regularly curved, and slightly thickened interiorly. The columella is nearly straight, with an inconspicuous tubercle about halfway, near the base with a rounded angle. The inside of the aperture is nacreous.

These deep-sea species are found and are endemic at hydrothermal vents. Their limpet-shaped shell consist of non-nacreous aragonite. The thick periostracum covers the shell edge. The apex is posterior, in some species projecting posteriorly, and deflected to the right.

Leiden Museum "Naturalis". Pearl Maxima is one of the largest true pearls or nacreous pearls in the world. This irregularly shaped pearl has a weight of 2385 grains (119.25 grams) and is 71 millimetres long. Its colour varies from cream to gold.

There is a small white spot at the base. The hindwings are bright nacreous (resembling mother of pearl). Adults have been recorded on wing from mid-July to mid-September. The larvae feed on the leaves of Silene ciliata and Petrocoptis pyrenaica.

The base is the same base color as the body, and the interior of the aperture is thinly nacreous (pearly). This species is often found without a periostracum. The operculum is circular, light brown, multispiral, and chitinous. Size range: 44 to 130 mm diameter.

Antennae, head, thorax and abdomen dark umber brown, paler beneath. Male sex-mark of form 2, the patch of specialized scales on both forewing and hindwing very small; the nacreous area surrounding the specialized scales on the underside of the forewing very pale brown.

The variegated surface is spirally ribbed. The large aperture is wider than the long, nacreous interior. The horny operculum is circular and multispiral.G.W. Tryon (continued by Pilsbry) (1890) Manual of Conchology XII Stomatellidae, Scissurellidae, Pleurotomariidae, Haliotidae, Scutellinidae, Addisoniidae, Cocculinidae, Fissurellidae The foot is truncated posteriorly.

The aperture is rounded-quadrangular. The thin upper margin is curved and runs uninterruptedly in the basal margin. The columellar margin is partly reflected over the umbilicus. The interior of the aperture is nacreous, with a few shallow grooves, corresponding to the stronger external lirae.

The three whorls are convex with the last whorl descending. The large aperture is very oblique, rounded-oval, nacreous, iridescent and slightly sulcate within, corresponding to the sculpture of the outside. The arcuate columella is narrow and flattened.G.W. Tryon (1890), Manual of Conchology vol.

Quadrula is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae native to rivers of the American Midwest and mid-south. All have thick nacreous shells with well-developed hinge teeth, many also with external shell sculpturing of nodules or lumps.

The shell shows a fine lamellar sculpture. The circular aperture is feebly nacreous. The thick peristome is continuous and shows a callous varix. The multispiral operculum is hispid, corneous and has a soft, calcareous outer layer (intritacalx) formed of pearly beads that are disposed spirally.

The first known owner of the pearl was Sir Hendrik Coenraad Sander, who auctioned the pearl in Amsterdam in 1778.A description and history of one of the largest nacreous pearls in the world. Journal of Gemmology 2009, vol. 31, no 5-8, pag.

Thebase of the shell is plano- convex. The oblique aperture is subrhomboidal. The throat is pearly and sulcate inside, brilliantly nacreous, the pearl not attaining to the edge of the lip, which is sharp and finely crenulated. The columellar margin is thick, subvertical, with a small tubercle.

The slightly nacreous shell reaches a length of 15 mm. It contains 6¼ whorls having the same general form as in Gaza fischeri, but with a more prominent nucleus. This nucleus is small, bulbous, and dark brown. The first 2½ whorls are glassy, brown spotted, smooth.

The lip is simple. The colors are arranged in radiating flammules, alternately white, strawberry-red, and pale flesh-color, gradually shaded into each other. On the base the dark or light-red are distributed along the granules in a somewhat articulated manner. The shell is nacreous beneath.

The inner edge of the outer lip is golden-brown and white, interior shining and nacreous. The operculum is horny multispiral with a central nucleus. Aradial cellular fringe-like film extends over the inner three-fourths of each spiral. The formula of the radula is ~ .1.5. 1.5.1. ~.

There is no umbilicus. The columella is short, straight, and ending in a slight knob inside the margin of the aperture. The aperture is crenulated by the sculpture, nacreous, obliquely set and subrectangular in form. The sutures are appressed, hardly visible except in the last three whorls.

The aperture is subquadrate, brilliantly nacreous with a narrow border. The base of the columella is externally expanded, internally bearing three small tubercles. The throat contains about seven entering ridges which commence at the bevel within the lip. The body whorl has a slight smear of callus.

The aperture is rounded-quadrate, oblique, less than ½ the total length of the shell. The outer lip is very narrowly black- edged. It isbordered by a series of short fine sulcations, beyond which there is a porcellaneous thickening. The throat is nacreous, iridescent, the reflections mainly green.

The sutures are plain. Other distinctive features include a smooth, green columella, an open, black-ringed umbilicus. The columellar margin is thickened at the base of the shell, and has a very obtuse tubercle there. The rounded- quadrangular aperture is angular above and brilliantly nacreous inside.

The round aperture is very slightly oblique, but on the pillar flattened, and at the point of it angulated slightly. It is nacreous within. Across the body there is no pad, but the shell is eroded, which looks like a thin callus. The outer lip is thin, not descending.

The body whorl descends anteriorly and is very broad. The oval aperture is finely sulcate within. It is nacreous, the predominant color being silvery or pinkish. The columella is a little expanded above, over a minute umbilical chink and surrounded by a crescentic opaque white, sharply defined tract.

The inner wall is smooth or transversely striate. The columella is emarginate, twisted, not thickened, ending in a round lump above the basal margin of the aperture. The oblique aperture is subrectangular, nacreous, sharp-edged, and crenulated by the ribs. The operculum is as usual in the genus.

Hood development may vary but is more pronounced in males. The hood normally takes a year to develop in young fry. Mature male lionheads periodically shed patches of their headgrowths. Lionheads can grow up to 6 inches (15 cm) in length (including finnage) and may have metallic, nacreous or matte scales.

The body whorl is provided with two .strong revolving ribs, one of which forms the periphery, while the other lies a little less than half wav from the first toward the oblique, round suture. The outer lip is sharp but strong. It is porcelaneous on the edge, brilliantly nacreous within.

The selenizone has 4 to 5 spiral cords and is usually concave in profile. The base is the same base color as the body, and the interior of the aperture is thinly nacreous (pearly). The operculum is roughly circular, light brown, multispiral, and chitinous. Size range: 64 to 175 mm diameter.

These bivalves are distinguished by having the two halves of the shell equally sized (i.e, they are equivalved) and having a few cardinal teeth separated from a number of long lateral teeth. Their shells lack a nacreous layer, and the gills are lamellibranch in form. Most species have a siphon.

The aperture is either oblong or transversely oval, and longer than wide or the reverse. The interior of the shell is nacreous. There is no operculum. Stomatia is closely allied to Stomatella, differing in the generally more elongated shell with a series of short folds or puckers below the sutures.

The columella is curved and slightly reflected at the upper part. The interior of aperture is smooth and nacreous. The operculum is many-whorled, outer 2 whorls broad;. The whorlsare sculptured by radiating and concentric striae, causing a latticed appearance, radiating striae stronger on the distal half of each whorl.

Ranchus may come in orange, red, white, red-and-white, blue, black, black-and-white, black-and-red, natural, and chocolate coloration. Scalation may either be metallic, nacreous (calico) or matte. Ranchus with a pale-yellow bodies and bright red heads are rare. Ranchus are well-adapted to water quality and pH fluctuations.

The flat base of the shell is very obsoletely lirate. Its middle portion (umbilical tract) is excavated, concave, strongly spirally grooved. The sculpture does not extend into the aperture nor to the edge of the columella, which is nacreous. The large aperture is very oblique, very iridescent and neither lirate nor toothed within.

The height of the shell attains 1 mm, its diameter 0.9 mm. The very small, white shell is umbilicate, turbinate, not nacreous, with a conic brownish spire. The first whorl appears to be smooth. On the second whorl fine radial folds or puckering appears below the suture, becoming coarser on the following whorl.

Towards the keel, a few undulating spiral striae appear. This sculpture is crossed by small radiating riblets. The aperture is rhomboidal, very oblique, with sharp edges and an internal nacreous layer, at some distance from the margin, with 10 lirae near this margin, and a groove corresponding to the keel. The basal margin is smooth.

Lysandra hispana, the Provence chalk-hill blue, is a butterfly of the family Lycaenidae. It is found in Spain, southern France and northern Italy. The wingspan is 16–18 mm. It is very similar to Lysandra coridon but is paler (greyer and duller, greyish pearly-blue, nacreous blue) with the distal margin more strongly spotted.

The shell grows to a height of 6.5 mm. The shell is a rather narrow flat-based cone that is sharply angulated. The shell is small, thin, delicate, smooth, glassy, and nacreous under a thin white calcareous surface. Sculpture: There are longitudinals, which are faint, hairlike and sinuated, showing the old lines of growth.

The body whorl is concave above. The compressed periphery is encircled by two rather obscure carinae. The base of the shell is slightly convex, with a narrow spiral groove bounding a central area which is covered by a thin, radiately rugose, purple and white callus. The aperture is rounded quadrate, nacreous and iridescent within.

Mineral makeup usually does not contain synthetic fragrances, preservatives, parabens, mineral oil, and chemical dyes. For this reason, dermatologists may consider mineral makeup to be gentler to the skin than makeup that contains those ingredients. Some minerals are nacreous or pearlescent, giving the skin a shining or sparking appearance. One example is bismuth oxychloride.

RT-PCR demonstrated that the transcript of aspein is expressed at the outer edge of the mantle, corresponding to the calcitic prismatic layer, but not at the inner part of the mantle, corresponding to the aragonitic nacreous layer. Aspein is likely responsible for directed formation of calcite in the shell of the pearl oyster Pinctada fucata.

The term 'veiltail' is commonly and erroneously applied to any goldfish displaying a long caudal, but true veiltails must have all the characteristics described above. Veiltails are available in many colors and may have either metallic or nacreous scales. They can grow from . They are not good swimmers but can be kept with other fancy goldfish.

Gaza daedala Drawing of apertural and apical view of a shell of Gaza daedala. (Original description by Watson) The height of the shell attains 20.6 mm, its diameter 17 mm. The thin shell has a depressedly globose shape with a convexly conical spire. It is translucent, horny, nacreous in its whole texture, and iridescent on the surface.

The shells of these mussels are variable in shape, but usually equivalve and elongate. They have solid, nacreous valves with a pearly interior, radial sculpture, and an entire pallial line. Freshwater mussel showing glossary of terms. Several species of freshwater pearl mussels collected in a river during a survey of the Marais des Cygnes National Wildlife Refuge.

The sculpture is composed of oblique, radiating striae, more prominent on the upper whorls. The base of the shell is almost smooth, with a slight stride of growth and very fine concentric lines. The nacreous aperture is obliquely quadrangular. The basal margin is continuous with the columella, and is not angulated at its junction with it.

The Palawan Princess, a five-pound non-nacreous pearl then considered the second largest, was offered at auction by Bonhams and Butterfields of Los Angeles on December 6, 2009. Estimated to fetch between $300,000 to $400,000, it passed unsold.Palawan Princess – 5 Pound Pearl – Up for Auction (archived from the original on 2016-01-16), karipearls.com, December 6, 2009.

Pinna is distinguished from its sibling genus Atrina by the presence of a sulcus dividing the nacreous region of the valves, and the positioning of the adductor scar on the dorsal side of shells. These bivalves most commonly stand point-first in the sea bottom in which they live, anchored by a net of byssus threads.

Shimmering Icefield () is an icefield between the Shipton and Tilman Ridges in the Allan Hills, Oates Land in East Antarctica. It was reconnoitered in 1964 by the New Zealand Antarctic Research Programme's Allan Hills Expedition, who gave the name because of its frequently nacreous luster when viewed against the sun.Shimmering Icefield Geographic Names Information System. United States Geological Survey.

Lenticular cloud over the Antarctic ice near Scott Base. Lenticular clouds (Latin: Lenticularis lentil-shaped, from lenticula lentil) are stationary clouds that form mostly in the troposphere, typically in perpendicular alignment to the wind direction. They are often comparable in appearance to a lens or saucer. Nacreous clouds that form in the lower stratosphere sometimes have lenticular shapes.

Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone, Oklahoma. Dated to the late Middle Pennsylvanian, which makes it by far the oldest deposit in the world with aragonitic nacreous shelly fossils.Buckhorn Lagerstätte of Oklahoma Click on photo for more information. Nacre is secreted by the epithelial cells of the mantle tissue of various molluscs.

Generally the family consists of species with elongate shells with notably unequal valves. Some of the genera have lost the small anterior auricle but all lack a byssal notch. The shell structuring consists of a regular prismatic calcitic outer layer and an interior layering which is nacreous. The valve surfaces show multiple pits where the valve ligaments were attached.

The peristome is thin, a trifle crenulated inside. The columella has a slight excavation, and is very bluntly nodulous near the base. The interior is brightly nacreous The shell color is typically a light yellowish-brown with irregular lighter, subsutural maculations, very occasionally with pink or purple beads or rarely a stripe. It has a peripheral circle of alternating chestnut and white spots.

The height of the shell attains 11 mm. The thin and slightly nacreous, imperforate shell has an ovate shape. The shell contains seven whorls, the first wound horizontally, thus giving the spire a decapitated aspect. The median whorls are separated by a channeled suture, flattened on the shoulder and subangled at the periphery, the last slightly descending behind the aperture.

Basilissopsis is a genus of sea snails, marine gastropod mollusks in the family Seguenziidae. In 1897 Dautzenberg and Fischer created this new genus for their specimen of Basilissopsis watsoni, based on the shell characteristics of discolored specimens that were non-nacreous and lacked labral sinuses.Dautzenberg and H. Fischer. 1897. Campagnes scientifiques de S. A. Ie Prince Albert l de Monaco.

Precious Wentletrap: the spiral shell of Epitonium scalare sea snail. The calcium carbonate layers in a shell are generally of two types: an outer, chalk-like prismatic layer and an inner pearly, lamellar or nacreous layer. The layers usually incorporate a substance called conchiolin, often in order to help bind the calcium carbonate crystals together. Conchiolin is composed largely of quinone-tanned proteins.

The shell is lusterless, red, marked at the suture, keel and base with olive or brown articulated with white. The surface is very rough, with a strong double nodulous keel at the middle of the whorl, several nodose spiral riblets and threads below it, strongly. The shell is plicate or puckered below the sutures. The aperture is irregular-oval and nacreous inside.

The shell is sculptured with about 5 lirulae, anteriorly granulose. The umbilicus is large, closely ornamented with about 3 spiral distant lines, and radiating costulations continued from the base. The umbilicus is bounded by a granular keel, but has three other distant spiral lines crossing the lirulae. The rounded aperture is indentated by the carinae, scarcely in contact parietally, iridescent inside and nacreous.

Anabarella is a species of bilaterally-flattened monoplacophoran mollusc, with a morphological similarity to the rostroconchs. Its shell preserves evidence of three mineralogical textures on its outer surface: it is polygonal near the crest of the shell, subsequently changing to both spiny and stepwise. Its internal microstructure is calcitic and semi-nacreous. Its name reflects its provenance from Anabar, Siberia.

The rest of the surface is smooth and shining, with a slight nacreous lustre and with numerous fine growth striae. The body whorl is conspicuously keeled below the periphery and with a second keel at some distance on the smooth base. The aperture is subrhombic. The outer margin is thin, angulate at the end of the lower row of nodules.

Oblique axial striae crowd between the granules on the spire, but are obsolete on the base. The aperture is quadrate oblique. The outer lip is crenulate, toothed just within the margin opposite each spiral lira, within this thickened and wrinkled, and in the throat lirate and nacreous. The basal lip is crenulate, thickened within with 5 teeth gradually enlarging towards the columella.

The shell is small, rudimentary, auriform (ear-shaped) and is situated far back on the animal. The shell is incapable of containing the body, and is reduced to the function of a shield for the lungs and heart. The shell is paucispiral, and is nacreous within. The columella is excavated into a pit for the reception of the shell- muscle.

Molluscs within this genus are characterized by elongated, wedge-shaped shells, distinguished from the genus Pinna by the lack of any grooves in the nacreous lining of the shell, and by the central positioning of the adductor scar. As with other pen shells (Pinnidae) they commonly stand point-first in the sea bottom in which they live, anchored by net of byssus threads.

The mineral found in nacre is aragonite, CaCO3, and it occupies 95% vol. Nacre is 3000 times tougher than aragonite and this has to do with the other component in nacre, the one that takes up 5% vol., which is the softer organic biopolymers. Furthermore, the nacreous layer also contains some strands of weaker material called growth lines that can deflect cracks.

The columella is concavely arched with a slight angle, not to be called a tooth, formed by the end of the umbilical carina at the base. The Interior is extremely nacreous. The operculum is amber-colored, fibrous toward the edges, with twelve or more whorls, a small central elevation on the inner side. The animal has a stout rounded muzzle, short stout tentacles and large black eyes.

Philobryidae is a taxonomic family of very small equivalved triangular saltwater clams, marine bivalve molluscs, related to the ark clams and the bittersweets. Their shells have projecting umbones and are non-nacreous. The ligament of the hinge is either completely internal or only slightly external. They have only one adductor muscle scar on the inside of each of their shells as opposed to the more-common two.

The shell can be anything from white through yellowish to a pale brownish-grey in colour, up to 6.5 cm in diameter. Its interior is nacreous and white or yellowish in colour. The shell is thin but quite deep, with circular closely packed growth ridges. It is a filter feeder, with long siphons, burying itself up to 20 cm deep in sand or mud.

The columella has a strong denticle. The colour of the shell is whitish with the inner nacre showing through, with vague brownish flames on specimens from shallower sites. The inside of the round aperture is nacreous. This species is distinguished from Danilia tinei in having the axial lamellae minute and about three times more numerous, the whitish colour and the more inflated and more fragile shell, with more convex whorls.

The base has 38 to 40 fine spiral threads. The protoconch and primary whorls are white and are smooth, the rest of the shell is creamy peach to white, or pale pink, with a slight iridescent sheen and occasional sparse pale reddish axial flammules. Occasionally the selenizone has thin orange lines. The base is the same color as the body, and the interior of the aperture is nacreous (pearly).

Pompoms may have either metallic or nacreous scalation, and can occur with or without a dorsal fin. It will be best if the lionhead variety of these fishes are engaged with the same variety or other dorsal fin less fishes. Free Information Keeping Pom Pom Goldfish The Chinese submit this variety as the "Velvet ball". There are records for the existence of this fish being seen as far back as 1898.

The small, high-spired shell has a conical shape and is flatly rounded on the base. It is white, dull on the surface, with a bright nacreous gleam shining through. Spirals: On the upper part of the body whorl there are two rows of tubercles, the first and weaker one is close up to the suture. The second is a little lower than the middle, and its tubercles are strong.

The base has strong spiral threads which are weakly beaded and is paler in color than the body, with scattered darker and lighter beads along the threads. The siphonal canal is closed and is ivory white near the aperture with a golden yellow to orange edge adjacent to the base. The aperture is white and nacreous. The size of the adult shell varies between 30 mm and 80 mm.

The surface of the shell is finely spirally striate, the striae about 8 on the body whorl, with a couple of stronger ribs at the periphery, which are visible above the suture on the spire whorls. The short spire is conic, acute, with its lateral outlines rectilinear. The 7–8 whorls are flat, the last one acutely carinated, and flat beneath. The oblique aperture is rhomboidal, smooth and nacreous within.

It is narrowly umbilicated, with a smooth epidermis, thin, but especially so on the base. The shell is more or less nacreous all over under a thin porcellanous upper layer. Sculpture: The first three whorls (after the embryonic apex) are reticulated by three sharp remote spirals, and rather stronger, slightly oblique longitudinals, which rise at their intersection into small sharp pyramidal tubercles. The interstices are a little broader than high.

The intersections of these two systems cut the whole surface into rhombic reticulations, whose breadth is about 0.28 mm and their height 0.15 mm. The longitudinal threads themselves are about 0.13 mm and the spirals about 0.077 mm broad. On the base, the longitudinals are flattened and spread out into undulations. Color: creamy, on a dull polished surface, with a faint nacreous gleam which is pearly within the mouth.

This is visible on the inside of the valve as an indentation on the pallial line which is known as the pallial sinus. The shell is composed of two calcareous valves held together by a ligament. The valves are made of either calcite, as is the case in oysters, or both calcite and aragonite. Sometimes, the aragonite forms an inner, nacreous layer, as is the case in the order Pteriida.

The axial threads form an overall continuous sigmoid pattern along the shell's longitudinal axis, and the spiral sculpture becomes gradually weaker toward the basal region of last whorl. The basal part of the shell is sculptured by 10-12 spiral cords, but the umbilical region is smooth, with a well-marked margin. The aperture is quadrangular, and bears three deep sinuses. The shell is colored glossy white, with a nacreous shade.

One of the largest gastropod shells found on the Southern California coast, this species varies between 40 mm and 145 mm. The shell lacks an umbilicus, and has a turbinate-conical shape. Like other shells of the family turbinidae it is composed of a thick inner nacreous layer, covered by a thinner porcellanous layer. In this species both are covered by a dark brown shaggy periostracum in life.

The base has 29 to 35 spiral ribs which are finely beaded. The protoconch and primary whorls are white and the rest of the shell is creamy overlaid with numerous irregular brown to purple-red axial flammules, the base is creamy with lighter brown to purple-red flammules, and the interior of the aperture is nacreous. The shell is regularly found without a periostracum. The operculum is small, roughly circular, dark brown, multispiral, and chitinous.

The composition of goslarite was determined by the US National Bureau of Standards (now the National Institute of Standards and Technology) in 1959 as follows: SO3 27.84 wt%, ZnO 28.30 wt% and 43.86 wt%. Goslarite's cleavage is perfect in {010}, as for epsomite and morenosite. The color of goslarite ranges from brownish to pinkish, blue, brown, colorless, green and green blue. The luster ranges from vitreous to nacreous and silky (if fibrous).

Laminates and composites made from nacreous shell and synthetic materials, described as "fake", "faux", or "shin paua", are sometimes used by luthiers. The channel cut for the inlay of purfling may increase the flexibility of the plates where they join the sides, affecting an instrument's pitch and sustain. In cases of heavy decorative inlay, the effective vibrational area of the sound board may be reduced. Today plastic purfling is commonplace in mass-produced instruments.

The surfaces of the valves have faint concentric sculpture lines and are covered in rows of fine granulations. The margins are smooth and the ligament is mostly internal. The right valve has a single cardinal tooth and the left valve has a ridge-like lateral tooth and a socket for the cardinal from the right valve. The inside of the valves is nacreous and the pallial line has a broad, shallow sinus.

Its upper insertion is carried far forward, connected with the lower by a thin dull film of callus. The lip is quite sharp, within a white edge is followed by a brown border anfl that again by a nacreous layer. This sequence again appears along the interior suture. The umbilicus forms a broad open funnel, penetrating to the initial whorl, margined by a beaded funicle which ends in an expansion on the columella base.

This rare, very fragile shell is brilliantly nacreous. Its colour is green, with violet and blue iris hues occurring. The somewhat fugitive outer cuticle shows rufous flames, depicted on a greyish ground.J.C. Melvill (1910), Descriptions of Twenty-nine Species of Marine Mollusca from the Persian Gulf, Gulf of Oman, and North Arabian Sea, mostly collected by Mr. F. W. Towns-end, of the Indo-European Telegraph Service; Annals & Magazine of Natural History vol.

The base of the shell, which is flatly rounded, has a narrow flattish margin, and in the middle a slight umbilical depression, in the centre of which is a minute umbilical hole almost covered by the columellar lip. The suture is linear. The aperture is scarcely oblique, and very slightly inclined out from the axial line. It is squarish, but rounded on the base and at the angles, a little broader than high, nacreous within.

The body whorl slightly descends at the aperture and is not eroded on the base. The large aperture is oblique. The outer lip is margined within with yellow and black, followed by a nacreous and then by an opaque white thickening which more or less contracts the aperture and which is more or less notched at about the place of the periphery. The columella is white, much narrower than in Diloma aethiops.

Colour: Theshell has a brownish yellow colour, but below the epidermis there is a thin pure white porcellanous layer, through which and the epidermis the sheen of the nacreous layer gleams. The base is whiter, the epidermis there being very thin. Inside, the aperture shows an exquisite roseate nacre. The spire is high, with a slightly concave contour, the lines of which are hardly swollen out by the slight tumidity of the body whorl.

The inner edge is bevelled, of a dull callus, radiately plicate, the margins united by a thick layer of callus, within brilliantly nacreous. An expansion of the columella slightly intrudes upon the umbilicus, which is narrow but deep, margined by a crenulate rib, internally with two deep-seated funicles. Charles Hedley, The Mollusca of Mast Head Reef, Capricorn Group, Queensland. Part II; Proceedings of the Linnean Society of New South Wales v.

The lip is edged inside by black, or black and white. The columella is arcuate, produced above in a heavy porcellanous callous deposit, half-surrounding the umbilicus and deeply notched in the middle. The shell of Cittarium pica presents a rather wide umbilicus, which is deep and devoid of sculpture, but spirally bicostate inside. The semicircular, oblique aperture is distinguishably nacreous inside as is the case in other Trochoidea, and is circular.

The shell is thinner and more nacreous than the typical form, and with the radiating and spiral sculpture not differing so much in strength.Dall W. H. 1889. Reports on the results of dredging, under the supervision of Alexander Agassiz, in the Gulf of Mexico (1877-78) and in the Caribbean Sea (1879-80), by the U.S. Coast Survey Steamer "Blake", Lieut.-Commander C.D. Sigsbee, U.S.N., and Commander J.R. Bartlett, U.S.N., commanding. XXIX.

The base is concentrically, rather deeply furrowed, the 6 furrows narrower than the intervening ridges. In the umbilicus, which perforates almost to the apex, all of the whorls are visible, encircled by an acute carina. The aperture is subquadrate, nacreous, smooth within, and has a groove indicating the place of the external keel. The columella is S-shaped, and ends in a blunt tooth, before which there is a small acute denticle.

They are most commonly seen with metallic scales colored shades of orange (called 'red' by fanciers), white, or red and white. Celestials with nacreous scales are known but rarely seen. Despite their limited vision and their lack of a dorsal fin, they are active and agile swimmers. They do require some special attention since, in addition to having easily damaged upward-oriented eyes (and, as a result, having limited vision), they are sensitive to cold water temperatures.

The aperture is rather oblique, a little higher than it is broad, slightly flattened above, and a very little angulated at the junction of the outer lip to the body. The thin lip is very little reflected on the umbilicus, porcellaneous on the edge, with a very slight pearly marginal callus, which is continuous across the body, and nacreous within. The large umbilicus is funnel-shaped, quickly contracting, but leaving the whole inner spire visible.Watson, R. B. 1879.

The Euomphalina comprise a major suborder of mainly Paleozoic archaeogastropods, shells of which are hyperstophic to depressed orthstrophic, commonly with an angulation at the outer upper whorl surface thought to be coincident with the exhalent channel; shell wall thick, outer layer calcitic, inner layers aragonitic but not nacreous; operculum calcareous and heavy. Their range is from the Upper Cambrian to the Triassic, and possibly as high as the Upper Cretaceous.J. Brooks Knight et al 1960. Systematic Descriptions (of gastropods).

The outer lip is on its outer part, inside the edge lined with mother-of-pearl, visibly furrowed.. On this part borders a white porcellanous coat, underneath standing out like a rib, on the base cut by two furrows. The throat is nacreous all around. The columella is compressed, flat, arcuate, produced into a sharp tooth below, and outwardly with a furrow parallel with its free margin. The color is black, with narrow white dense zig-zag curved streaks.

The larvae of the golden mussel are small (around 100 micrometers), and live in the water column until they are ready to settle. The size of adult individuals is usually around 20–30 mm in length, but specimens up to over 45 mm have been reported. The outer surface of the shell is golden to dark brown, whereas internally it is nacreous, pearly white to purple. The valves are very thin and brittle, and there are no hinge teeth.

The stratospheric temperature profile creates very stable atmospheric conditions, so the stratosphere lacks the weather-producing air turbulence that is so prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds and other forms of weather. However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft.

The shell is creamy yellow overlaid with many crimson axial flammules above and below the selenizone which has yellowish orange crescent shaped growth marks, the base is a pale creamy yellow with occasional light crimson flammules, and the interior of the aperture is nacreous. The shell is occasionally found with part of its dark brown periostracum near the margin opposite the aperture. The operculum is small, dark brown, multispiral, and chitinous. Size range: 45 to 129 mm diameter.

While biologists would regard this object as a kind of pearl, gemologists regard it as a non-nacreous pearl, lacking the iridescence of the pearls that come from saltwater pearl oysters and freshwater pearl mussels. Because of its great size, a giant clam can create a very large pearl, but not an iridescent, gemlike one. The Gemological Institute of America (GIA) and CIBJO now simply use the term "pearl" (or, where appropriate, the more descriptive term "non-nacreous pearl") when referring to such items, rather than the term "calcareous concretion"The Pearl Book , International Jewellery Confederation.GIA Gems & Gemology magazine news archive, December 3, 2008 (archived from the original on 2008-12-04) and, under U.S. Federal Trade Commission rules, various mollusk pearls may be referred to as "pearls" without qualification.Guides for the Jewelry, Precious Metals, and Pewter Industries Gemologist Michael Steenrod in Colorado Springs has appraised the pearl at $60,000,000 (1982) and $93,000,000 (2007). Another 1982 appraisal, by Lee Sparrow who owned a gem laboratory and appraisal business in the Phelan Building in San Francisco, put the pearl at $42,000,000.

The shell surface is generally smooth, ornamentation consisting of fine transverse lyrae or growth lines parallel to the aperture lip.J. Brooks Knight et al 1960. Systematic Descriptions (Gastropoda), Treatise on Invertebrate Paleontology, Part I, Mollusca 1, R.C. Moore (ed). The Anomphalidae differ from the Euomphalcea to which they have been reassigned Anomphalidea in Paleobio database in being more trochoidal, in lacking the angulation on the upper whorl surface characteristic of Euomphalacea, and in having the inner shell layer seemingly nacreous.

Euomphaloid shells are mostly discoidal and may be either orthostrophic (coils wrapped around an erect cone) or hyperstrophic (coils wrapped around an inverted cone); are widely umbilicate and commonly have a channel, presumed exhalent, within the angulation in the outer part of the upper whorl surface. The shell wall is relatively thick, with an external prismatic layer of calcite, which may be pigmented, and an internal layer of lamellar, but not nacreous, aragonite.(1960). Treatise on Invertebrate Paleontology. Part I, Gastropoda.

The oe which defines the umbilicus is more sharply beaded than the rest. Longitudinals: Below the suture and near the umbilicus the surface is sharply but delicately puckered, and these puckerings, strong in the early whorls, are in the later faintly continued across the whorls as lines of growth. The colour of the shell is yellowish white, with a brilliant nacreous sheen shining through the thin superficial calcareous layer, which becomes more opaque in drying. The high spire is scalar.

The spirals, of which there are about fifteen, are closer set, broader and flatter, except the first three below the carina, which are sharp and narrow. The whole base of the shell is pit-marked from the spiral interstitial furrows being cut up by the longitudinals. The color of the shell is dead white (on the base a little glossy) on the thin porcelaneous surface, through which ihe nacreous layer behind gleams. The spire is raised, with a very slightly concave outline.

In most marine mussels the shell is longer than it is wide, being wedge-shaped or asymmetrical. The external colour of the shell is often dark blue, blackish, or brown, while the interior is silvery and somewhat nacreous. The common name "mussel" is also used for many freshwater bivalves, including the freshwater pearl mussels. Freshwater mussel species inhabit lakes, ponds, rivers, creeks, canals, and they are classified in a different subclass of bivalves, despite some very superficial similarities in appearance.

The aperture is oblique above, arching more nearly to a perpendicular below. smoothly, evely reflected and thickened from the columella to the suture, with an internal channel behind the thickening. The columella is callous above, thinly and unevenly reflected half-way across the umbilicus, gently and very obliquely descending and smoothly passing into the basal part of the lip. The interior of the aperture, the lip, the umbilical callus, and a slight wash near the sutural junction, are brilliantly nacreous.

The precursor to the Bubble Eye, known as the Toadhead or hama-tou, had upturned eyes and very small, bladder-like sacs. Through selective breeding, the bubble eye is currently available with either a long or more rounded body and the choice between matte, metallic or nacreous scales. A recent development of the bubble eye has four eye sacs rather than the usual two.See photo number 6 Desirable colors for these fish include red, calico, orange, red and white, and the rare black.

The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as mother of pearl. The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging debris by entombing them in successive layers of nacre, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called encystation and it continues as long as the mollusc lives.

Intermediate grades have ranges of 240–180°. ; Brightness of colors (iridescence) : The brightness of colors and their iridescence is essentially dependent on how well-preserved the nacreous shell is, and how fine and orderly the layers of aragonite are. The quality of the polish is also a factor. The "dragon skin" cracking usually hinders its value; the most prized ammolite is the sheet type (see formation) that has broad, uninterrupted swathes of color similar to the "broad flash" category of opal.

Both contain organic components (proteins, sugars and lipids) and the organic components are characteristic of the layer, and of the species. The structures and arrangements of mollusc shells are diverse, but they share some features: the main part of the shell is a crystalline Ca carbonate (aragonite, calcite), despite some amorphous Ca carbonate occurs; and despite they react as crystals, they never show angles and facets. The examination of the inner structure of the prismatic units, nacreous tablets, foliated laths... shows irregular rounded granules.

The aperture is subcircular, straighter on the side of the slightly concave columella, which forms a conspicuous angle with the basal margin. The parietal wall has a thin layer of enamel, forming a small projection, covering part of the umbilicus. The interior of the nacreous aperture is smooth, and has a flattened rib near the outer and basal margin. It differs from the allied species, by the rows of short scales, and from all the preceding species, by the rounded periphery of the body whorl.

Imitation pearls are also widely sold in inexpensive jewelry, but the quality of their iridescence is usually very poor and is easily distinguished from that of genuine pearls. Pearls have been harvested and cultivated primarily for use in jewelry, but in the past were also used to adorn clothing. They have also been crushed and used in cosmetics, medicines and paint formulations. Whether wild or cultured, gem-quality pearls are almost always nacreous and iridescent, like the interior of the shell that produces them.

Whether wild or cultured, gem-quality pearls are almost always nacreous and iridescent, like the interior of the shell that produces them. However, almost all species of shelled mollusks are capable of producing pearls (technically "calcareous concretions") of lesser shine or less spherical shape. There is a lot of myth and legend surrounding some of these pearls. The Pearl of Lao Tzu for a long time thought to be the largest Pearl had its history fabricated by a conman by the name of Victor Barbish.

There are three types of PSC clouds—nitric acid trihydrate clouds, slowly cooling water-ice clouds, and rapid cooling water-ice (nacreous) clouds—provide surfaces for chemical reactions whose products will, in the spring lead to ozone destruction. The photochemical processes involved are complex but well understood. The key observation is that, ordinarily, most of the chlorine in the stratosphere resides in "reservoir" compounds, primarily chlorine nitrate () as well as stable end products such as HCl. The formation of end products essentially removes Cl from the ozone depletion process.

Perlucin encourages carbonate deposition, and is found at the interface of the chitinous and aragonitic layer in some shells. An acidic shell matrix appears to be essential to shell formation, in the cephalopods at least; the matrix in the non-mineralized squid gladius is basic. In oysters and potentially most molluscs, the nacreous layer has an organic framework of the protein MSI60, which has a structure a little like spider silk and forms sheets; the prismatic layer uses MSI31 to construct its framework. This too forms beta-pleated sheets.

The aperture is slightly oblique, but with a perpendicular columella, round, and nacreous within. The outer lip is thin, transparently porcelaneous on the edge, but thickened by nacre within. The columellar region of the inner lip is perpendicular, rounded within the aperture, advancing to a sharp point in front, slightly reverted but not appressed, having a small open furrow and a minute umbilical chink behind it. This species extremely resembles Calliostoma occidentale (Mighels & C. B. Adams, 1842), but it is smaller and broader in proportion, with a less high spire.

These pearls, which are often pink in color, are a by-product of the conch fishing industry, and the best of them display a shimmering optical effect related to chatoyance known as 'flame structure'. Somewhat similar gastropod pearls, this time more orange in hue, are (again very rarely) found in the horse conch Triplofusus papillosus. The second largest pearl known was found in the Philippines in 1934 and is known as the Pearl of Lao Tzu. It is a naturally occurring, non-nacreous, calcareous concretion (pearl) from a giant clam.

Nautilus half-shell showing the camerae in a alt=Section cut of a nautilus shell Nautiluses are the sole living cephalopods whose bony body structure is externalized as a planispiral shell. The animal can withdraw completely into its shell and close the opening with a leathery hood formed from two specially folded tentacles. The shell is coiled, aragonitic, nacreous and pressure-resistant, imploding at a depth of about . The nautilus shell is composed of two layers: a matte white outer layer, and a striking white iridescent inner layer.

The best specimens have been used to create necklaces and earrings. A conch pearl is a non-nacreous pearl (formerly referred to by some sources as a 'calcareous concretion'); it differs from most pearls that are sold as gemstones in that it is not iridescent. The specific weight of the conch pearl is 2.85, notably heavier than any other type. Due to the sensitive nature of the animal and the location of the pearl-forming portion of the snail within the spiral shell, commercial cultivation of pearls is considered virtually impossible.

The effect of adularescence, also commonly referred to as schiller or shiller, is best described as a milky, bluish luster or glow originating from below the surface of the gemstone. The schiller, appearing to move as the stone is turned (or as the light source is moved), gives the impression of lunar light floating on water (accounting for moonstone's name).Long, Bill (2004), "Varieties of Light II: Pleochroism, Nacreous, Adularescence, A(d)venturescence." Though white schiller is the most common, in rarer specimens, orange or blue lusters are produced.

The daisy stingray, Dasyatis margarita, is a little-known species of stingray in the family Dasyatidae, found in shallow waters along the coast of West Africa. This species typically grows to across and has a rounded pectoral fin disc and (in adults) a wide band of dermal denticles over its back. It is characterized by a greatly enlarged, nacreous denticle in the middle of its back called a "pearl spine"; this feature is shared with the similar but much smaller pearl stingray (D. margaritella), which has often been confused with this species.

The pearl stingray (Dasyatis margaritella) is a little-known species of stingray in the family Dasyatidae, found in shallow coastal waters from Mauritania to Angola. Growing to across, this species has a rounded pectoral fin disc with a pointed snout, and a wide band of dermal denticles over the back in adults. It closely resembles and is often confused for the much larger daisy stingray (D. margarita); both species are characterized by the presence of an enlarged, nacreous denticle in the middle of the back called a "pearl spine".

The internal ligament is supported by a diagonal ridge of shell and there are no teeth near the hinge. The exterior of the shell is white, slightly granular and sculptured with fine concentric lines. The interior of the shell is somewhat nacreous, with two adductor muscle scars and a pallial line that is slightly concave at the anterior end and has a broad pallial sinus at the posterior end. There is a gape at both ends of the shell and a pair of long siphons emerge from the posterior end being fused for their full length.

This volute is known to produce pearls; however the Melo melo pearl has no nacre, unlike the pearl of a pearl oyster. The GIA and CIBJO now simply use the term 'pearl' (or, where appropriate, the more descriptive term 'non-nacreous pearl') when referring to such items, rather than the previously-used term 'calcareous concretion'CIBJO 'Pearl Book' – Natural, Cultured & Imitation Pearls — Terminology & Classification (2007-05-1) GIA 'Gems & Gemology' magazine news archive and, under Federal Trade Commission rules, various mollusc pearls may be referred to as 'pearls' without any qualification.Guides for the Jewelry, Precious Metals, and Pewter Industries. Ftc.gov (30 May 1996).

These objects used to be referred to as "calcareous concretions" by some gemologists, even though a malacologist would still consider them to be pearls. Valueless pearls of this type are sometimes found in edible mussels, edible oysters, escargot snails, and so on. The GIA and CIBJO now simply use the term 'pearl' (or, where appropriate, the more descriptive term 'non-nacreous pearl') when referring to such items and, under Federal Trade Commission rules, various mollusk pearls may be referred to as 'pearls', without qualification. A few species produce pearls that can be of interest as gemstones.

This oyster along with the Pacific wing-oyster (Pteria sterna) was the subject of a pearl fishery in the Gulf of California since before the arrival of Hernando Cortez in 1535. The Spaniards quickly appreciated the value of the harvest and in 1586 declared the gathering of oysters to be a right of the Spanish crown. By the 1840s, the export of the shells was as valuable as the pearls extracted from them; the nacreous shells were used to make mother-of- pearl buttons for clothing. In 1874, compressed air diving equipment made harvesting the oysters easier.

The oblique aperture is subangulate, black-rimmed and crenulated on the thin edge of the outer lip. It is nacreous, silvery white toward the edge, bright lustrous golden yellow within and around the umbilical region, which latter though deeply pitted is not open. The white columella has a callus and is arcuated with a moderately developed rib bounding the umbilical depression and terminating in a single tubercle. This rib is paralleled by a shallow furrow terminating in a notch just below the tubercle, and by an exterior or outer ridge, part of the way double, of a brilliant orange color.

A second book, The Polar Aurora (Oxford Press, 1955), contains both his experimental work on aurorae and his mathematical attempts to model them. In his review of this book, Canadian astronomer John F. Heard calls Størmer "the acknowledged authority" on aurorae. Heard writes, "The Polar Aurora will undoubtedly remain for many years a standard reference book; it belongs on the desk of anyone whose work or interest is involved with aurorae." Other astrophysical phenomena investigated by Størmer include pulsations of the earth's magnetic field, echoing in radio transmissions, nacreous clouds and luminous night clouds, zodiacal light, meteor trails, the solar corona and solar vortices, and cosmic rays.

Natural (or wild) pearls, formed without human intervention, are very rare. Many hundreds of pearl oysters or mussels must be gathered and opened, and thus killed, to find even one wild pearl; for many centuries, this was the only way pearls were obtained, and why pearls fetched such extraordinary prices in the past. Cultured pearls are formed in pearl farms, using human intervention as well as natural processes. One family of nacreous pearl bivalves – the pearl oyster – lives in the sea, while the other – a very different group of bivalves – lives in freshwater; these are the river mussels such as the freshwater pearl mussel.

Harrison rented a ramshackle cottage near the Brittany town of Beg-Meil, and each evening raced to the dunes to watch the sun set over the ocean. In late-summer 1896, he was joined there by struggling writer Marcel Proust and composer Reynaldo Hahn. He opened their eyes to how light plays on water: > We have seen the sea successively turn blood red, purple, nacreous with > silver, gold, white, emerald green, and yesterday we were dazzled by an > entirely pink sea specked with blue sails.Hahn to Marie Nordlinger, quoted > in William C. Carter, Marcel Proust, A Life (New Haven, Connecticut: Yale > University Press, 2000), p. 197.

The independent origins of this trait are further supported by crystallographic differences between clades: the orientation of the axes of the deposited aragonite 'bricks' that make up the nacreous layer is different in each of the monoplacophora, gastropods and bivalves. Mollusc shells (especially those formed by marine species) are very durable and outlast the otherwise soft- bodied animals that produce them by a very long time (sometimes thousands of years even without being fossilized). Most shells of marine molluscs fossilize rather easily, and fossil mollusc shells date all the way back to the Cambrian period. Large amounts of shell sometimes forms sediment, and over a geological time span can become compressed into limestone deposits.

Colours are produced when a material is scored with fine parallel lines, formed of one or more parallel thin layers, or otherwise composed of microstructures on the scale of the colour's wavelength. Structural coloration is responsible for the blues and greens of the feathers of many birds (the bee-eater, kingfisher and roller, for example), as well as many butterfly wings, beetle wing-cases (elytra) and (while rare among flowers) the gloss of buttercup petals. These are often iridescent, as in peacock feathers and nacreous shells such as of pearl oysters (Pteriidae) and Nautilus. This is because the reflected colour depends on the viewing angle, which in turn governs the apparent spacing of the structures responsible.

Female has the upperside similar to that of the wet-season form but the black area on both forewings and hindwings much restricted just as it is in the male. The underside is also similar to that of the wet-season form but on the forewing the curved black band is very much narrower, and the nacreous surface of the hindwing has more or less of a yellowish tinge. In both sexes and in both seasonal forms the antennae are black minutely speckled with white, the tufted hair on the head and thorax anteriorly greyish green, abdomen white; beneath: head and thorax pale yellowish white, abdomen white. The wingspan is 65–76 mm.

The mantle edge secretes a shell (secondarily absent in a number of taxonomic groups, such as the nudibranchs) that consists of mainly chitin and conchiolin (a protein hardened with calcium carbonate), except the outermost layer, which in almost all cases is all conchiolin (see periostracum). Molluscs never use phosphate to construct their hard parts, with the questionable exception of Cobcrephora. While most mollusc shells are composed mainly of aragonite, those gastropods that lay eggs with a hard shell use calcite (sometimes with traces of aragonite) to construct the eggshells. The shell consists of three layers: the outer layer (the periostracum) made of organic matter, a middle layer made of columnar calcite, and an inner layer consisting of laminated calcite, often nacreous.

Females of the octopus genus Argonauta secrete a specialized paper-thin egg case in which they reside, and this is popularly regarded as a "shell", although it is not attached to the body of the animal and has a separate evolutionary origin. The largest group of shelled cephalopods, the ammonites, are extinct, but their shells are very common as fossils. The deposition of carbonate, leading to a mineralized shell, appears to be related to the acidity of the organic shell matrix (see Mollusc shell); shell-forming cephalopods have an acidic matrix, whereas the gladius of squid has a basic matrix. The basic arrangement of the cephalopod outer wall is: an outer (spherulitic) prismatic layer, a laminar (nacreous) layer and an inner prismatic layer.

The shell has a typical trochoid shape with a spire angle of approximately 72 degrees and nearly smooth sided until the body whorls which are slightly inflated at the shoulder with a rounded periphery. The base is moderately convex to flat, and the shell has a large nacreous (pearly) columellar callus which covers about one third of the base and can be keeled at its outer margin. The aperture is oval, the slit is positioned mid whorl and is long, about 16 to 20 percent of the circumference. The shell is heavily textured with about 20 spiral cords crossed by numerous fine crescent shaped axial growth lines above the selenizone (the area where the shell growth filled in the slit) and about 10 spiral cords below.

Some of these crosses tend to be less animated swimmers, especially those that possess a short, sharply downturned, ranchu- like caudal peduncle with flared and short caudal fins, traits which are otherwise uncharacteristic for the breed. Such fish can be quite sedentary, spending most of their time at or near the bottom of the aquarium; however, a more expansive color range can be found among these hybrids, with metallic specimens appearing in chocolate, black and various bi-colors in addition to the standard metallic colors, and nacreous fish seen in bi-color, tri-color and calico. These hybrids are not generally available commercially outside Asia but can be acquired through specialist dealers and importers. The Deme- ranchu is identical to the Celestial in conformation save for its telescopic eyes which do not turn upward.

The fossil record shows that all molluscan classes evolved some 500 million years ago Hugh and Marguerite Stix, Robert Tucker Abbott (1991), The Shell: Five Hundred Million Years of Inspired Design; Bdd Promotional Book CoISBN 978-0792447160 from a shelled ancestor looking something like a modern monoplacophoran, and that modifications of the shell form ultimately led to the formation of new classes and lifestyles.e.g. However, a growing body of molecular and biological data indicate that at least certain shell features have evolved many times, independently. The nacreous layer of shells is a complex structure, but rather than being difficult to evolve, it has in fact arisen many times convergently. The genes used to control its formation vary greatly between taxa: under 10% of the (non-housekeeping) genes expressed in the shells that produce gastropod nacre are also found in the equivalent shells of bivalves: and most of these shared genes are also found in mineralizing organs in the deuterostome lineage.

The serrated spine of the cowtail stingray is potentially dangerous, and this species is regarded as particularly dangerous to handle as its long tail is capable of reaching over its back to strike someone gripping it from the front. Small to moderate numbers of cowtail stingrays are caught as bycatch in trawls and marketed for meat throughout their range, and their tough skin is used to polish wood. This species is also the primary source of shagreen or galuchat, a type of leather, for which it has been valued since ancient times due to the large size and regular arrangement of its dorsal tubercles (called "pearls" in the trade from their nacreous appearance after being rubbed down, hence the old name "pearled ray"). A boom in the international shagreen trade since the 1990s, with the material being used in many fashion accessories from wallets to fancy pens, has led to enormous numbers of cowtail stingrays being harvested in Southeast Asia.

Edvard Munch, 1921 In his diary in an entry headed "Nice 22 January 1892", Munch wrote: He later described his inspiration for the image: Among theories advanced to account for the reddish sky in the background is the artist's memory of the effects of the powerful volcanic eruption of Krakatoa, which deeply tinted sunset skies red in parts of the Western hemisphere for months during 1883 and 1884, about a decade before Munch painted The Scream. This explanation has been disputed by scholars, who note that Munch was an expressive painter and was not primarily interested in literal renderings of what he had seen. Another explanation for the red skies is that they are due to the appearance of nacreous clouds which occur at the latitude of Norway and which look remarkably similar to the skies depicted in The Scream.The Sky in Edvard Munch's The Scream Alternatively, it has been suggested that the proximity of both a slaughterhouse and a lunatic asylum to the site depicted in the painting may have offered some inspiration.