agate
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agate
Agate
a mineral; a variety of chalcedony in the form of a dense, cryptocrystalline aggregate of fibrous or radial quartz formations (Si02)—so-called quartzite or α-tridymite. The mineral is characterized by multiple interstratification of thin (up to 10 microns), variously colored layers. The hardness of agate on the mineralogical scale is 6.0–6.5. The following varieties are recognized depending on the combination of colors in the layers—onyx (white and black layers), carnelian (red and white), sardonyx (reddish brown and white), and agates (bluish gray and white). Agate occurs in veins, in geodes, in amygdules among igneous rocks, and in the tuffs of the last. It is used as an industrial or semiprecious stone and in the manufacture of technical articles (bearing stones, prisms for scales, and so on). Agate is colored artificially to obtain bright, decorative forms.
G. P. BARSANOV