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agate

(Encyclopedia) agate ăg´ĭt [key], translucent, cryptocrystalline variety of quartz and a subvariety of chalcedony . Agates are identical in chemical structure to jasper, flint, chert, petrifi...

Brewer's: Agate

Ag′ate(2 syl.). So called, says Pliny (xxxvii. 10), from Achates or Gagates, a river in Sicily, near which it is found in abundance. These, these are they, if we consider we…

onyx

(Encyclopedia) onyx ŏn´ĭks [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 st...

chalcedony

(Encyclopedia) chalcedony kălsĕd´ənē [key] [from Chalcedon ], form of quartz the crystals of which are so minute that its crystalline structure cannot be seen except with the aid of a microscope. ...

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, SiO 2. It occurs in crystals of th...

Scottsbluff

(Encyclopedia) Scottsbluff skŏts´blŭf˝ [key], city (1990 pop. 13,711), Scotts Bluff co., W Nebr., on the North Platte River near the Wyo. line; inc. 1900. It is the market, distribution, and processing p...

Petrified Forest National Park

(Encyclopedia) Petrified Forest National Park, 93,533 acres (37,881 hectares), E Ariz.; est. as a national monument 1906, designated a national park 1962. A part of the Painted Desert, it contains the largest...