|
|
| |
|
|
| |
QUARTZ AND OTHER SILICA MINERALS |
|
| |
|
|
| |
Quartz is the most abundant mineral in the Earth’s continental crust (although feldspar is more common in the world as a whole). It is made up of a lattice of silica (SiO2) tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm3.Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. These veins may bear precious metals such as gold or silver, and form the quartz ores sought in mining. Erosion of pegmatites may reveal expansive pockets of crystals, known as “cathedrals.”
Quartz is a common constituent of granite, sandstone, limestone, and many other igneous, sedimentary, and metamorphic rocks.
|
|
| |
|
|
| |
|
|
| |
| Major Varieties |
| Chalcedony |
Any cryptocrystalline quartz, although generally only used for white or lightly colored material. Otherwise
more specific names are used.
|
| Agate |
Multi-colored, banded chalcedony, semi-translucent to translucent |
| Onyx |
Agate where the bands are straight, parallel and consistent in size. |
| Jasper |
Opaque chalcedony, typically red to brown |
| Aventurine |
Translucent chalcedony with small inclusions (usually mica) that shimmer. |
| Tiger’s eye |
Fibrous gold to red-brown coloured quartz, exhibiting chatoyancy. |
| Rock crystal |
Clear, colorless |
| Amethyst |
Purple, transparent |
| Citrine |
Yellow to reddish orange to brown, greenish yellow |
| Prasiolite |
Mint green, transparent |
| Rose quartz |
Pink, translucent, may display diasterism |
| Rutilated quartz |
Contains acicular (needles) inclusions of rutile |
| Milk quartz |
White, translucent to opaque, may display diasterism |
| Smoky quartz |
Brown to grey, opaque |
| Morion |
Dark-brown, opaque |
| Carnelian |
Reddish orange chalcedony, translucent |
|
|
|
|
|
|
|
