The crystalline form of silicon dioxide (SiO2), one of the most common minerals in the Earth's crust. The clear crystals are known as rock crystal, but it is commonly white and translucent. Semi-precious varieties (eg amethyst) may be coloured. It may occur as microcrystalline varieties, such as chalcedony, agate, and flint. It is very important industrially because of its piezo-electric properties.
| Quartz | |
|---|---|
| General | |
| Category | Mineral |
| Chemical formula (or Composition) | Silica (silicon dioxide, SiO2) |
| Identification | |
| Color | Clear (if no impurities); also see Varieties |
| Crystal habit | 6-sided prism ending in 6-sided pyramid (typical) |
| Crystal system | Hexagonal |
| Cleavage | None |
| Fracture | Conchoidal |
| Mohs Scale hardness | 7 - lower in impure varieties |
| Luster | Vitreous/glossy |
| Refractive index | 1.544-1.553 - DR +0.009 (B-G interval) |
| Pleochroism | None |
| Streak | White |
| Specific gravity | 2.65 constant; variable in impure varieties |
| Melting point | 1650 (±75) °C |
| Boiling point | 2230 °C |
| Solubility | H2O insoluble |
| Major varieties | |
| Chalcedony | Any cryptocrystalline quartz, although generally only used for white or lightly coloured material. |
| Agate | Banded Chalcedony, translucent |
| Onyx | Agate where the bands are straight, parallel and consistent in size. |
| Jasper | Opaque chalcedony, impure |
| Aventurine | Translucent chalcedony with small inclusions (usually mica) that shimmer. |
| Rock Crystal | Clear, colourless |
| Ruby Quartz | Crimson glass-like crystal, absorbs vast amounts of solar energy |
| Amethyst | Purple, transparent |
| Citrine | Yellow to reddish orange, greenish yellow |
| Prasiolite | Mint green, transparent |
| Rose quartz | Pink, translucent, may display diasterism |
| Milk quartz, or snow quartz | White, translucent to opaque, may display diasterism |
| Smoky quartz | Brown, transparent |
| Morion | Dark-brown, opaque |
| Carnelian | Reddish orange chalcedony, translucent |
Quartz is one of the most common minerals in the Earth's continental crust.
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