White opal

Arsenic with lead oxide White opal... 

Phosphoric acid Nickel oxides and cobalt oxides An ingredient of white opal glass or promotes transparency to u.v. or opacity to i.r. when used with ferrous iron Brown, purple, deep blue... 

Marquis reagent. 1 ml of formalin solution in 10 ml of concentrated sulfuric acid. The reagent is poured over the chromatogram (which must be thoroughly dry) supported on a sheet of white opal glass. 

Opal White opal Opaque, porcelain-like white material colors resemble flashes or speckles... 

FIGURE 5.12 Striking reflection colors can be seen in this white opal, a naturally occurring colloidal crystal. 

Appearance Milky white, opal, or yellowish emulsion... 

Weight percent of opal in surface marine sediments (generally 0 to 5 cm). White areas indicate no data. Source From Seiter, K., et al. (2004). Deep-Sea Research I 51, 2001-2026. 

Gaseous emanations near the surface are known to produce opal or cristobalite (microcrystalline) (Kesler, 1970 Steiner, 1953 Schoen and White, 1965) and quartz or amorphous silica at greater depth (Keller and Hanson, 1968 Fournier, 1967). 

Opal is a hydrous silica (Si02), sometimes thought of as an amorphous silica gel. It is a fairly soft gem, measuring only 5 to 6 on the Mohs scale. It is relatively common in nature except in its precious form, which comes mainly from Australia. In Switzerland, since 1970, opal of precious quality has been made synthetically. Usually cut in the cabochon shape to permit its rainbowlike display of color, opals come in white, black, and fire varieties. Black opals are dark gray to blue, and fire opals, which are more transparent than other opals, are usually orange-red in color. 

Opalescence is a pearly or milky internal reflection, most common in white or light-colored minerals such as some opal or moonstone (albite or ortho-clase feldspar). This is also known as adularescence. Like iridescence and play of color, these properties are not consistent within any natural material, and can only be used to describe individual specimens. Some synthetic materials have been created specifically to display these properties and so always show them. 

Precious opal is usually defined by the background color, black, white, or fire (orange). There are terms used to describe the distribution of the internal colors, and which colors are dominant. 

A combination of several different opaline materials may be found juxtaposed. For example, in fossilized wood both tridymite and crystobalite may be determined in a sample whde adjacent portions of the sample may be composed of opal-A. The silicified wood may be transparent or translucent, clear and colorless, or white, yellow, red, brown, and black, indicating inclusions of other, usually iron-containing, complexes during precipitation of the colloid or gel. The faithfully preserved structures of fossilized wood suggest that the replacement phenomena are molecule-by-molecule processes that take place under low temperamres and pressures, and require concomitant removal of nonsiliceous compounds but do not disrupt the ceUularity of the woody tissues. Alternatively, primary... 

Jars Parallel side cylindrical containers bearing no shoulder. Used mainly for creams and ointments. May be white flint, amber or opal glass. 

Stn. Silica.—This acid is found pure in rock crystal, or in white quartz. Along vrith small and variable quantities of certain metallic oxides it forms many well-known minerals—as yellow or smoke rock crystal with oxide of iron agate, jasper, heliotrope, camelian, with the same metal amethyst with oxide of manganese prase with oxide of nickel rose-quartz with some fugitive colouring matter opal and calcedony with water, c. c. Many sands and sandstones are nearly pure silica, and quartz rock and flint are quite pure. 

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