Quartz

Hardness: 7 (Mohs scale); Color: Variable, common colors include colorless, white, gray, purple (amethyst), pink (rose quartz), brown, black. The specimen appears to be white to grayish-white; Luster: Vitreous (glassy); Crystal structure: Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Quartz is one of the most common minerals in the Earth's crust. It forms in a wide range of geological environments. It can crystallize from magma, especially in igneous rocks like granite and rhyolite. It also forms from hydrothermal solutions, filling veins and cracks, or from precipitation in sedimentary environments (e.g., chert, sandstone). It is also a major component of many metamorphic rocks (e.g., quartzite, schist, gneiss). Its geological age varies greatly depending on the specific rock or deposit it's found in, ranging from Precambrian to recent.

Quartz has numerous uses: In industry, it's used in glass manufacturing, abrasives, electronics (osciillators, resonators), and as a raw material for ceramics. As gemstones, varieties like amethyst, citrine, rose quartz, and smoky quartz are highly valued for jewelry. Sandstone, largely composed of quartz, is a common building material. Pure quartz crystals can be used in optical instruments.

Quartz is the second most abundant mineral in the Earth's continental crust. Its piezoelectric properties (generating an electric charge in response to mechanical stress) make it vital for electronic devices like watches, radios, and computers. It is remarkably resistant to weathering, which is why it's a primary constituent of sand in rivers and beaches.

In the field, quartz is identified by its hardness (scratches glass and steel), glassy luster, lack of cleavage (fractures conchoidally), and typically hexagonal crystal shape (though often found in massive or granular forms like the specimen shown). It is very common and can be found globally in almost all types of rocks. It's abundant in igneous rocks, sedimentary rocks (as sand and gravel), and metamorphic rocks. For collectors, well-formed crystals and colored varieties are most prized. The specimen appears to be a massive form of white or milky quartz.