Agate
Rock consisting of cryptocrystalline silica alternating with microgranular quartz / From Wikipedia, the free encyclopedia
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For other uses, see Agate (disambiguation).
Agate (/ˈæɡɪt/ AG-it) is the banded variety of chalcedony,[1] which comes in a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate was common in Ancient Greece, in assorted jewelry and in the seal stones of Greek warriors,[2] while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus Valley civilisation.
Quick Facts General, Category ...
Agate | |
---|---|
General | |
Category | Chalcedony variety |
Formula (repeating unit) | SiO2 (silicon dioxide) |
Crystal system | Trigonal or monoclinic |
Identification | |
Color | banded |
Crystal habit | Cryptocrystalline silica |
Cleavage | None |
Fracture | Conchoidal, with very sharp edges |
Mohs scale hardness | 6.5–7 |
Luster | Waxy |
Streak | White |
Diaphaneity | Translucent |
Specific gravity | 2.58–2.64 |
Refractive index | 1.530–1.540 |
Birefringence | up to +0.004 (B-G) |
Pleochroism | Absent |
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