Quartz

Hardness: 7 on Mohs scale. Color: colorless, white, purple (amethyst), pink (rose quartz), gray, brown, black (smoky quartz), yellow (citrine). 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 crystallizes from magma in igneous rocks (like granite and pegmatite), precipitates from hot hydrothermal solutions in veins, and is a major component of many metamorphic rocks (like quartzite) and sedimentary rocks (like sandstone). Its formation can span billions of years, from early Earth to present day.

Industry: electronics (oscillators, filters), glass manufacturing, abrasives (sandpaper, grinding media), sandpaper, optical instruments. Jewelry: varieties like amethyst, citrine, rose quartz, smoky quartz, and clear quartz are widely used as gemstones. Construction: Sandstone (composed largely of quartz) is used as building material; quartz sand is used in concrete and mortar.

Quartz is one of the most abundant minerals in the Earth's continental crust. Its piezoelectric properties (generating electric charge when stress is applied) make it crucial for electronic components. Amethyst, a purple variety of quartz, was once as valuable as rubies and emeralds.

Field Identification: High hardness (scratches glass), conchoidal fracture (shell-like breaks), vitreous luster, and often characteristic hexagonal crystal habit (though often found anhedral or massive). Common Locations: Found globally in various rock types, including igneous, metamorphic, and sedimentary rocks. Significant deposits are found in Brazil, Arkansas (USA), and parts of Europe and Africa. Tips for Collectors: Look for well-formed crystals in pegmatites and hydrothermal veins. Color varieties are often sought after.