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quartz
(Encyclopedia)quartz, one of the commonest of all rock-forming minerals and one of the most important constituents of the earth's crust. Chemically, it is silicon dioxide, SiO2. It occurs in crystals of the hexagon...jasper, type of quartz
(Encyclopedia)jasper, opaque, impure cryptocrystalline quartz, usually red, but also yellow, green, and grayish blue. It is used as a gem. Ribbon jasper has the colors in stripes. ...quartzite
(Encyclopedia)quartzite, usually metamorphic rock composed of firmly cemented quartz grains. Most often it is white, light gray, yellowish, or light brown, but is sometimes colored blue, green, purple, or black by ...rock crystal
(Encyclopedia)rock crystal: see quartz.amethyst
(Encyclopedia)amethyst ămˈəthĭst [key] [Gr.,=non-drunkenness], variety of quartz, violet to purple in color, used as a gem. It is the most highly valued of the semiprecious quartzes. It is associated with a num...enamelware
(Encyclopedia)enamelware, utensils having a metal foundation and a coating of special glass, called porcelain enamel, applied by fusion. The porcelain enamel, or vitreous enamel, is applied to make the utensils cor...cat's-eye
(Encyclopedia)cat's-eye, gemstone that displays a thin band of reflected light on its surface when cut as a cabochon. Its name is derived from its supposed resemblance to the eye of a cat. The optical effect, known...sandstone
(Encyclopedia)sandstone, sedimentary rock formed by the cementing together of grains of sand. The usual cementing material in sandstone is calcium carbonate, iron oxides, or silica, and the hardness of sandstone va...onyx
(Encyclopedia)onyx ŏnˈĭks [key], variety of cryptocrystalline quartz, differing from agate only in that the bands of which it is composed are parallel and regular. Its appearance is most striking when the bands ...gneiss
(Encyclopedia)gneiss nīs [key], coarse-grained, imperfectly foliated, or layered, metamorphic rock. Gneiss is characterized by alternating light and dark bands differing in mineral composition and having coarser g...Browse by Subject
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