Opal Wikipedia. Opal. A rich seam of irridescent opal encased in matrix. General. Category. Mineraloid. Formularepeating unitHydratedsilica. Si. O2n. H2. OCrystal system. Amorphous1Identification. Color. Colorless, white, yellow, red, orange, green, brown, black, blue, pink. Crystal habit. Irregular veins, in masses, in nodules. Cleavage. None1Fracture. Conchoidal to uneven1Mohs scale hardness. Computer Jargon Dictionary. You certainly have noticed that there is lots and lots of strange gibberish associated with computers and the industry just loves. Luster. Subvitreous to waxy1Streak. White. Diaphaneityopaque, translucent, transparent. Specific gravity. Density. 2. 0. 9Polish luster. Vitreous to resinous1Optical properties. Single refractive, often anomalous double refractive due to strain1Refractive index. Mexican opal may read as low as 1. Birefringencenone1Pleochroism. None1Ultravioletfluorescenceblack or white body color inert to white to moderate light blue, green, or yellow in long and short wave, may also phosphoresce, common opal inert to strong green or yellowish green in long and short wave, may phosphoresce fire opal inert to moderate greenish brown in long and short wave, may phosphoresce1Absorption spectragreen stones 6. Diagnostic featuresdarkening upon heating. Jerry Lee Lewis All Killer No Filler RARE. Solubilityhot salt water, bases, methanol, humic acid, hydrofluoric acid. References23Opal is a hydratedamorphous form of silica Si. O2n. H2. O its water content may range from 3 to 2. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. Your Ultimate Pulp and Paper Dictionary on the Web. Common Dreams Meaning Interpretations. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A. Un libro un insieme di fogli, stampati oppure manoscritti, delle stesse dimensioni, rilegati insieme in un certo ordine e racchiusi da una copertina. He sends all sorts of loving wishes for Christmas, and an especial message to you girls, said Mrs. In cryptography, a bruteforce attack consists of an attacker trying many passwords or passphrases with the hope of eventually guessing correctly. Precious opal shows a variable interplay of internal colors, and though it is a mineraloid, it has an internal structure. At microscopic scales, precious opal is. A aa aah aahed aahing aahs aal aalii aaliis aals aargh aarrgh aarrghh aas ab aba abaca abacas abaci aback abacus abaft abaka abakas abalone abamp abamps abandon abas. IWBjj-Surh4/hqdefault.jpg' alt='Magenta Dictionary Crack' title='Magenta Dictionary Crack' />It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia. The internal structure of precious opal makes it diffract light. Depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the black opals are the rarest, whereas white and greens are the most common. Opals vary in optical density from opaque to semitransparent. Precious opaledit. Precious opal consists of spheres of silicon dioxide molecules arranged in regular, closely packed planes. Idealized diagram. Multicolor rough crystal opal from Coober Pedy, South Australia, expressing nearly every color of the visible spectrum. Precious opal shows a variable interplay of internal colors, and though it is a mineraloid, it has an internal structure. At microscopic scales, precious opal is composed of silica spheres some 1. It was shown by J. V. Sanders in the mid 1. The regularity of the sizes and the packing of these spheres determines the quality of precious opal. Where the distance between the regularly packed planes of spheres is around half the wavelength of a component of visible light, the light of that wavelength may be subject to diffraction from the grating created by the stacked planes. The colors that are observed are determined by the spacing between the planes and the orientation of planes with respect to the incident light. The process can be described by Braggs law of diffraction. Visible light cannot pass through large thicknesses of the opal. This is the basis of the optical band gap in a photonic crystal. The notion that opals are photonic crystals for visible light was expressed in 1. Vasily Astratovs group. In addition, microfractures may be filled with secondary silica and form thin lamellae inside the opal during solidification. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, which is correctly termed play of color. Contrarily, opalescence is correctly applied to the milky, turbid appearance of common or potch opal. Potch does not show a play of color. For gemstone use, most opal is cut and polished to form a cabochon. Solid opal refers to polished stones consisting wholly of precious opal. Opals too thin to produce a solid may be combined with other materials to form attractive gems. An opal doublet consists of a relatively thin layer of precious opal, backed by a layer of dark colored material, most commonly ironstone, dark or black common opal potch, onyx, or obsidian. The darker backing emphasizes the play of color, and results in a more attractive display than a lighter potch. An opal triplet is similar to a doublet, but has a third layer, a domed cap of clear quartz or plastic on the top. The cap takes a high polish and acts as a protective layer for the opal. The top layer also acts as a magnifier, to emphasize the play of color of the opal beneath, which is often of lower quality. Triplet opals therefore have a more artificial appearance, and are not classed as precious opal. Jewelry applications of precious opal can be somewhat limited by opals sensitivity to heat due primarily to its relatively high water content and predisposition to scratching. Combined with modern techniques of polishing, doublet opal produces a similar effect to black or boulder opal at a fraction of the price. Doublet opal also has the added benefit of having genuine opal as the top visible and touchable layer, unlike triplet opals. Common opaledit. White and blue opal from Slovakia. Besides the gemstone varieties that show a play of color, the other kinds of common opal include the milk opal, milky bluish to greenish which can sometimes be of gemstone quality resin opal, which is honey yellow with a resinous luster wood opal, which is caused by the replacement of the organic material in wood with opal 9menilite, which is brown or grey hyalite, a colorless glass clear opal sometimes called Mullers glass geyserite, also called siliceous sinter, deposited around hot springs or geysers and diatomite or diatomaceous earth, the accumulations of diatom shells or tests. Other varieties of opaledit. Brightness of the fire in opal ranges on a scale of 1 to 5 5 being the brightest1. Fire opal is a transparent to translucent opal, with warm body colors of yellow to orange to red. Although it does not usually show any play of color, occasionally a stone will exhibit bright green flashes. The most famous source of fire opals is the state of Quertaro in Mexico these opals are commonly called Mexican fire opals. Fire opals that do not show play of color are sometimes referred to as jelly opals. Mexican opals are sometimes cut in their rhyolitic host material if it is hard enough to allow cutting and polishing. This type of Mexican opal is referred to as a Cantera opal. Also, a type of opal from Mexico, referred to as Mexican water opal, is a colorless opal which exhibits either a bluish or golden internal sheen. Girasol opal is a term sometimes mistakenly and improperly used to refer to fire opals, as well as a type of transparent to semitransparent type milky quartz from Madagascar which displays an asterism, or star effect, when cut properly. However, the true girasol opal1. It is not a play of color as seen in precious opal, but rather an effect from microscopic inclusions. It is also sometimes referred to as water opal, too, when it is from Mexico. The two most notable locations of this type of opal are Oregon and Mexico. Peruvian opal also called blue opal is a semiopaque to opaque blue green stone found in Peru, which is often cut to include the matrix in the more opaque stones. It does not display play of color. Blue opal also comes from Oregon in the Owyhee region, as well as from Nevada around the Virgin Valley. Sourcesedit. Polished opal from Yowah Yowah Nut1. Queensland. Australian opal has often been cited as accounting for 9. South Australia accounting for 8. Recent data suggests that the world supply of precious opal may have changed. In 2. 01. 2, Ethiopian opal production was estimated to be 1. United States Geological Survey. USGS data from the same period 2. Australian opal production to be 4. Common Dreams Meaning Interpretations.