Chemical Formula |
SiO2 |
Composition |
Silicon dioxide |
Color |
White, blue, red, green, yellow, orange, brown, pink, purple, gray, black, colorless, and multicolored. Often banded in many different color combinations, and a few rarer forms are iridescent. |
Streak |
White |
Hardness |
7 |
Crystal System |
Hexagonal |
Crystal Forms |
Chalcedony, being a microcrystalline variety of the mineral Quartz, does not occur in visible crystals. It occurs in botryoidal, mammilary, stalactitic, massive, nodular forms, as smooth rounded pebbles, asbanded masses, as amygdules, and as the linings of geodes. |
Transparency |
Transparent to opaque |
Specific Gravity |
2.6 - 2.7 |
Luster |
Vitreous, waxy, or dull |
Cleavage |
None |
Fracture |
Conchoidal |
Tenacity |
Brittle |
Other ID Marks |
1) Commonly fluorescent, usually green or white. |
Complex Tests |
Dissolves in hydrofluoric acid |
In Group |
Silicates; Tectosilicates; Silica Group |
Striking Features |
Hardness and form |
Environment |
Occurs in all mineral environments, especially in igneous environments. |
Rock Type |
Igneous, Sedimentary, Metamorphic |
Popularity (1-4) |
1 |
Prevalence (1-3) |
1 |
Demand (1-3) |
1 |
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