Quartz (likely)

Hardness: 7 (Mohs scale), Color: Varies widely, including brown, yellow, pink, purple, gray, white, Luster: Vitreous to greasy, Crystal structure: Hexagonal (trigonal), Cleavage: None, 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), precipitate from hydrothermal solutions in veins, or recrystallize during metamorphism in metamorphic rocks (e.g., gneiss, schist). It is also highly resistant to weathering, making it a common constituent of sedimentary rocks (e.g., sandstone) and alluvial deposits. Its geological age varies greatly depending on the specific formation event, ranging from Precambrian to recent.

Industry: Used in electronics (oscillators, filters), optics (lenses, prisms), abrasives, glassmaking, and ceramics. Jewelry: Many colorful varieties (amethyst, citrine, rose quartz) are popular gemstones. Construction: Sandstone (composed largely of quartz) is used as a building material. Collecting value: Well-formed crystals or rare varieties are highly prized by collectors.

Quartz is one of the most abundant minerals in Earth's crust. It is a main component of many rocks and is found in diverse geological settings. Amethyst, citrine, rose quartz, and smoky quartz are well-known varieties of quartz, distinguished by their color and microscopic inclusions. It is known for its piezoelectric properties (generates an electric charge under mechanical stress) and pyroelectric properties (generates an electric charge when heated), making it valuable in electronics.

Identify in the field: Look for its hardness (scratches glass), vitreous luster, lack of cleavage, and common crystal habits (hexagonal prisms with pyramidal terminations, though the pictured sample is tumbled/rounded). Color can vary, but the sample's brownish-yellow hue is consistent with some quartz varieties or stained quartz. Common locations: Found worldwide in virtually every type of rock. Large deposits are found in Brazil, Arkansas (USA), and various parts of Europe and Asia. Tips for collectors: Quartz is often found in riverbeds and beaches as pebbles due to its durability. Look for translucent to opaque samples with a somewhat greasy to glassy feel.