Smoky Quartz

Hardness: 7 on the Mohs scale. Color: Appears dark, likely black or very dark brown/purple, which is common for smoky quartz. Luster: Vitreous (glassy). Crystal Structure: Trigonal. Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.65.

Formed through hydrothermal processes in igneous and metamorphic rocks, as well as in pegmatites. The dark color is typically attributed to natural irradiation of clear quartz containing aluminum impurities. Geological Age: Varies widely, as quartz is a common mineral formed over billions of years throughout Earth's history.

Predominantly used as a gemstone in jewelry, often faceted as seen in the image, or cut as cabochons. It is also used for ornamental carvings, spiritual practices, and as collector's specimens due to its aesthetic appeal and crystal forms.

Smoky quartz is a very common and popular variety of quartz. Its color is due to natural irradiation of silicon dioxide, which creates color centers involving aluminum impurities within the crystal structure. This process can occur naturally in the Earth's crust as a result of exposure to gamma radiation from radioactive minerals. In some cases, clear quartz can be artificially irradiated to produce smoky quartz for commercial purposes. It is often found in large, well-formed crystals.

Can be identified in the field by its characteristic dark color (ranging from light smoky brown to opaque black), vitreous luster, and hardness (scratches glass). It often forms in prismatic crystals with hexagonal cross-sections and pyramid terminations. Commonly found in granites, pegmatites, and other igneous and metamorphic rocks, as well as in alluvial deposits. Notable localities include Brazil, the Swiss Alps, Scotland (where it is known as Cairngorm), the United States (Colorado, Arkansas), and Madagascar. For collectors, look for well-formed crystals and good clarity.