Quartz

Hardness: 7 on the Mohs scale. Color: Often colorless, but can also be milky white, grey, brown, violet (amethyst), pink (rose quartz), yellow (citrine), or black (smoky quartz). Luster: Vitreous (glassy). Crystal Structure: Hexagonal (trigonal crystal system). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Quartz forms in a wide range of geological environments. It can crystallize from magma (igneous), precipitate from hydrothermal solutions (hydrothermal), or form through regional and contact metamorphism (metamorphic). It is also very resistant to weathering, making it a common detrital mineral in sedimentary rocks. Its formation spans across all geological ages, from Precambrian to recent.

Industry: Components in electronics (oscillators, filters), abrasive in sandpapers and cutting tools, production of glass, ceramics, and cement. Construction: A major component of sand and gravel used in concrete and mortar. Jewelry: Many varieties are popular gemstones (e.g., amethyst, citrine, rose quartz, smoky quartz).

Quartz is one of the most abundant minerals in the Earth's continental crust, second only to feldspar. Its piezoelectric properties make it valuable in electronics for frequency control, such as in watches and radios. Large, flawless quartz crystals are rare in nature. Many varieties of quartz are used as semi-precious gemstones.

Identify in the field by its hardness (scratches glass), glassy luster, lack of cleavage (will fracture unevenly, often conchoidally), and hexagonal crystal shape if well-formed. It's commonly found in igneous rocks (granite, rhyolite), metamorphic rocks (gneiss, schist, quartzite), and sedimentary rocks (sandstone, chert). Tips for collectors: Look for crystal faces, observe its transparency or translucency, and test its hardness. It can be found globally, often in pegmatites, hydrothermal veins, and in riverbeds as water-worn pebbles.