Quartz

Hardness: 7 (Mohs scale), Color: Varies widely, including white, gray, brown, black, green, blue, pink, red, yellow. The specimen appears dark gray/brown. Luster: Vitreous (glassy) to waxy. Crystal Structure: Trigonal. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Quartz typically forms from the cooling of magma (igneous), precipitation from hydrothermal solutions (hydrothermal), or weathering and metamorphism of other rocks (sedimentary/metamorphic). It can also form at low temperatures in sedimentary environments. Its geological age varies significantly depending on the specific formation event, from billions of years to very recent.

Industry: Used in electronics (oscillators, filters), glassmaking, abrasives, and refractory materials. Construction: A major component of sand and gravel, used in concrete and mortar. Jewelry: Gemstone varieties are highly valued. Collecting Value: Both common and rare forms are collected.

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

Field Identification: Look for its hardness (scratches glass), conchoidal fracture (shell-like breaks), and vitreous luster. It does not react with acid. Common Locations: Found globally in almost all rock types. It's a fundamental component of granite, sandstone, and gneiss. Tips for Collectors: Look for well-formed crystals in vugs and veins, or for interesting color variations in massive forms. The specimen appears to be a weathered or river-tumbled piece of massive quartz, possibly chert or jasper (microcrystalline quartz) due to its dark color and somewhat dull appearance, although it's difficult to be certain without additional tests.