agate

agate

agate (ăgˈĭt), translucent, cryptocrystalline variety of quartz and a subvariety of chalcedony. Agates are identical in chemical structure to jasper, flint, chert, petrified wood, and tiger's-eye, and are often found in association with opal. The colorful, banded rocks are used as a semiprecious gemstone and in the manufacture of grinding equipment. An agate's banding forms as silica from solution is slowly deposited into cavities and veins in older rock. The stones can be artificially stained to produce combinations of color more vivid than those found in the natural state. The cutting and staining of agates has long been centered at Idar-Oberstein, Germany. Important sources of agate are Brazil, Uruguay, and the United States (Oregon, Washington, and around Lake Superior). The moss agate or mocha stone contains visible impurities in the form of dendritic shapes that resemble moss. See onyx.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

agate

[′ag·ət]

(graphic arts)

A type size in printing of about 5½ points, where 72 points equals 1 inch.

(mineralogy)

SiO₂ A fine-grained, fibrous variety of chalcedony with color banding or irregular clouding.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

agate

symbolizes health; supposed to relieve snake and scorpion bites. [Class. and Medieval Legend: Leach, 27]

See: Health

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agate

confers this power. [Rom. Folklore: Brewer Dictionary,15]

See: Invisibility

Allusions—Cultural, Literary, Biblical, and Historical: A Thematic Dictionary. Copyright 2008 The Gale Group, Inc. All rights reserved.

agate

1. an impure microcrystalline form of quartz consisting of a variegated, usually banded chalcedony, used as a gemstone and in making pestles and mortars, burnishers, and polishers. Formula: SiO₂

2. a playing marble of this quartz or resembling it

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005