Quartz

Hardness: 7 on the Mohs scale. Color: Often colorless, but can be white, grey, yellow, brown, pink, purple, green, or black due to impurities. Luster: Vitreous (glassy) to greasy. Crystal Structure: Hexagonal (trigonal system). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Quartz typically forms in igneous rocks (e.g., granite, pegmatite) during the cooling of magma, in metamorphic rocks (e.g., quartzite, gneiss) under high temperature and pressure conditions, and in sedimentary rocks (e.g., sandstone, chert) through the weathering of pre-existing rocks and subsequent cementation or precipitation from solutions. It can form over a wide range of geological ages, from Precambrian to recent.

Industry: Used in electronics (oscillators, filters), optics (lenses, prisms), abrasives, and as a component in glass, ceramics, and cement. Jewelry: Many varieties are used as gemstones (e.g., amethyst, citrine, smoky quartz, rose quartz). Construction: Main component of sand and sandstone, used as aggregate in concrete and mortar. Collecting: Popular among mineral collectors due to its wide variety of forms and colors.

Quartz is one of the most abundant minerals in the Earth's continental crust. It forms at all temperatures and is abundant in igneous, metamorphic, and sedimentary rocks. Many varieties of quartz exist, some of which are semi-precious gemstones (e.g., amethyst, citrine, rose quartz). Pure quartz is called rock crystal and is colorless and transparent.

To identify quartz in the field, look for its characteristic hardness (it will scratch glass and steel), glassy luster, and conchoidal (shell-like) fracture. It often forms well-defined hexagonal crystals, though in many rocks it appears as an anhedral (irregularly shaped) grain. It is extremely common and found globally in almost all rock types. Tips for collectors include looking for distinct crystal habits in vugs or veins, and variations in color or clarity which might indicate a specific quartz variety.