Chemical Formula |
SiO2 |
Composition |
Silicon dioxide. Its purple coloring is usually caused by impurities of iron or manganese compounds. |
Color |
Light to dark purple. Sometimes banded with purple and whitish lines. May also be mixed together with Citrine. |
Streak |
White |
Hardness |
7 |
Crystal System |
Hexagonal |
Crystal Forms |
Most often as protruding clusters of pyramids on a matrix base. These "pyramids" can be quite large. Also occurs as tall prismatic crystals, as short stubby crystals, in drusy aggregates, massive, in geodes, and as rounded waterworn stones. A very interesting habit is as crystalline crusts inside volcanic pipes. Crystals are usually striated horizontally, and occasionally have a scepter growth. |
Transparency |
Transparent to translucent |
Specific Gravity |
2.6 - 2.7 |
Luster |
Vitreous |
Cleavage |
Indiscernible |
Fracture |
Conchoidal |
Tenacity |
Brittle |
Other ID Marks |
Occasionally fluorescent cream or white in shortwave ultraviolet light. |
Complex Tests |
Dissolves in hydrofluoric acid. |
In Group |
Silicates; Tectosilicates; Silica Group |
Striking Features |
Color, crystal habits, and hardness. |
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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