Quartz

Hardness: 7 (Mohs scale), Color: Varies widely, often clear, white, gray, smoky (as seen in the image), purple (amethyst), yellow (citrine), pink (rose quartz), Luster: Vitreous (glassy), Crystal Structure: Hexagonal (rhombohedral crystal system), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Quartz forms in a wide range of geological environments. It can crystallize directly from magma in igneous rocks (e.g., granite, rhyolite), precipitate from hydrothermal solutions in veins, or form through the recrystallization of silica in metamorphic rocks (e.g., quartzite). It is also a primary component of many sedimentary rocks like sandstone. Its geological age varies greatly depending on the specific rock formation.

Industry: Used in electronics (oscillators, filters), optics (lenses, prisms), abrasives, and as a component in glass and ceramics. Construction: A major component of concrete, mortar, and asphalt. Jewelry: Many varieties are popular gemstones. Collecting: Valued by mineral collectors for its crystals and diverse forms.

Quartz is one of the most common minerals on Earth, making up about 12% of the Earth's crust. It is highly resistant to weathering, which contributes to its abundance in sedimentary rocks and sands. Many varieties of quartz are prized as gemstones, including amethyst, citrine, rose quartz, and smoky quartz.

Identify in the field: Look for its hardness (scratches glass and steel), glassy luster, and conchoidal (shell-like) fracture when broken. It does not exhibit cleavage. The specimen in the image appears to be a common, somewhat weathered piece of quartz or quartzite, given its grayish, somewhat translucent appearance and chunky form. Common locations: Found globally in almost all types of rocks and geological settings. Abundant in igneous, metamorphic, and sedimentary rocks, particularly in granite, gneiss, schist, and sandstone. Tips for collectors: Search in pegmatites for large crystals, in hydrothermal veins for well-formed specimens, and in riverbeds or beaches for water-worn pebbles.