Quartz

Hardness: 7 (Mohs scale). Color: Colorless, white, milky, or various shades (rose, smoky, amethyst, citrine) depending on impurities. Luster: Vitreous (glassy) to waxy. Crystal structure: Hexagonal (trigonal). Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.65.

Quartz is one of the most abundant minerals in the Earth's crust. It forms in a wide variety of geological environments. It can crystallize from magma (igneous rocks like granite), precipitate from hydrothermal solutions (veins, geodes), or form during metamorphic processes (quartzite) and sedimentary processes (sandstone). Its formation can span across all geological ages, from Precambrian to recent.

Industry: Silicon source, manufacture of glass, ceramics, abrasives, and electronics (quartz oscillators, transducers). Jewelry: Many varieties are popular gemstones (e.g., amethyst, citrine, smoky quartz, rose quartz). Construction: Main component of sand and gravel used in concrete and mortar. Used as decorative stones. Collecting value: Well-formed crystals and rare varieties are highly sought after by collectors.

Quartz is piezoresistive and piezoelectric, meaning it can generate an electric charge when subjected to mechanical stress, and vice-versa. This property makes it valuable in electronic devices. It is the second most abundant mineral in the Earth's continental crust, after feldspar. The term 'quartz' comes from the German 'Quarz'.

To identify in the field: Look for its characteristic hardness (scratches glass and steel), glassy luster, and the tendency to form hexagonal prisms with pyramidal terminations (though the piece shown is a fragment). It does not have cleavage, but breaks with a conchoidal fracture. Check for its variable color (from clear to milky white is common). Common locations: Found globally in almost all types of rocks: igneous (granite, rhyolite), metamorphic (gneiss, schist, quartzite), and sedimentary (sandstone, chert). Widely distributed in river sands and gravels. Tips for collectors: Look for clear, well-formed crystals in vugs and veins. Check for color variations to find more valuable specimens like amethyst or citrine. The specimen shown appears to be a clear to milky white, irregular fragment, consistent with common quartz.