Quartz

Hardness: 7 (Mohs scale), Color: Varies widely, including colorless, white, purple (amethyst), pink (rose quartz), brown (smoky quartz), green (aventurine), yellow (citrine), black (morion). The color in the image appears to be a dark, translucent grey or greenish-brown, which is consistent with smoky quartz or a heavily included common quartz. Luster: Vitreous (glassy). Crystal Structure: Hexagonal (trigonal system). Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.65.

Quartz forms under a wide range of temperatures and pressures and is found in igneous, metamorphic, and sedimentary rocks. In igneous rocks, it crystallizes from silicic magmas (e.g., granite). In metamorphic rocks (e.g., quartzite), it forms during regional or contact metamorphism. In sedimentary rocks (e.g., sandstone), it is often a primary detrital mineral due to its stability. The specific specimen appears to be a water-worn pebble, indicating it has been transported and rounded by processes like river flow or glacial movement, meaning it could originate from any of these rock types. Geological Age: Quartz itself doesn't have a specific geological age, as it forms continuously throughout Earth's history.

Industry: Used in glassmaking, abrasives, electronics (piezoelectric properties for oscillators and filters), and as a raw material for ceramics. Jewelry: Many varieties are popular gemstones (e.g., amethyst, citrine, rose quartz, smoky quartz). Construction: A major component of sand and gravel used in concrete, mortar, and asphalt. Used as an aggregate in many building materials.

Quartz is one of the most common minerals on Earth's crust, second only to feldspar. Its name comes from the German 'quarz', which itself has Slavic origins. Different varieties of quartz have been used for tools, jewelry, and spiritual purposes for thousands of years. Amethyst, citrine, and rose quartz are popular gemstone varieties.

Identification in the field: High hardness (scratches most other common minerals), vitreous luster, conchoidal fracture, and the absence of cleavage are key identifiers. It often forms glassy, often somewhat hexagonal, crystals if not extensively weathered. As a pebble, its rounded shape suggests erosional transport. The translucent to opaque appearance in shades of grey, brown, or greenish-brown is common for pebbles of common quartz. Common locations: Found globally in almost all geological environments – in granites, gneisses, sandstones, quartz veins, and riverbeds. Tips for collectors: Look for distinct crystal forms in geodes or veins; river and beach pebbles are often rounded quartz due to its resistance to weathering and abrasion.