Composition: Silicon dioxide (SiO2)
| Milky Quartz|
| Smoky Quartz|
Color: White, colorless, gray, yellow to orange-yellow, purple, violet, pink, gray-brown to brown, black
Streak: White; faintly tinted in color varieties
Luster: Vitreous, greasy, waxy
Tenacity: Brittle, tough
Specific Gravity: 2.65-2.66
Cleavage: Generally none
Habit: Crystals are short to long prismatic, pyramidal, distorted, twisted, bent, skeletal, and as druses. Aggregates are massive, coarse to granular, stalactitic, concretionary, and as sand.
Quartz is one of the most abundant minerals of the earth's crust, being an important constituent of many types of rocks and the major constituent in most sand. It is a hard, brittle mineral that has no apparent cleavage. Like glass, it breaks with a characteristic conchoidal fracture. It cannot be scratched with a knife, as can many of the minerals with which it might be confused, and it will easily scratch glass. Most people have picked up or seen quartz crystals, which are characteristic six-sided prisms terminated by six-sided pyramids. Such crystals usually are clear and colorless, although some are gray (smoky quartz) or violet (amethyst). But crystal faces develop only in special environments, such as open fissures or cavities in rock, and most quartz occurs as disseminated irregular grains in many different types of rocks. It also occurs as massive white aggregates of irregular grains, such as milk-y vein quartz. Quartz is much more resistant to alteration by weathering than are most other minerals, so it is a prominent constituent of beach and stream gravels, and smaller grains accumulate as sand. Quartz is mined for a wide variety of industrial uses. Large quantities are processed in the manufacture of glass and ceramic materials, and are used in the manufacture of cement and as a metallurgical flux. Carefully cut sections of clear quartz crystals are used as crystal oscillators to control the frequency of radio transmitters, and clear or attractively colored crystals are cut for gem stones. In many places veins of milky quartz contain disseminated gold or minerals of other valuable metals. Where the content of one or more valuable metals is sufficiently high, such veins are mined.
California Counties in Which this Mineral is Found
San Luis Obispo
Information on Specimen Photo:
Specimen Description: Quartz, El Dorado County. California Division of Mines and Geology Library.
Photographer: Max Flanery, CGS.