Smoky Quartz

Hardness: 7 on Mohs scale. Color: Brown-gray to black, often translucent. Luster: Vitreous (glassy). Crystal structure: Hexagonal (trigonal system). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Smoky quartz forms in igneous or metamorphic rocks rich in silica. Its coloration is believed to be caused by natural irradiation of silicon dioxide, which converts trace amounts of aluminum within the quartz structure into a color center. This process can occur over long geological periods or be induced artificially. It's often found in pegmatites, hydrothermal veins, and granite intrusions.

Primarily used in jewelry for beads, pendants, and carvings due to its attractive color and durability. It's also used as an ornamental stone and in some metaphysical practices. Historically, it was used in optical instruments and as a gemstone.

Smoky quartz is the official state gemstone of New Hampshire. It's sometimes called 'Smoky Topaz' or 'Cairngorm' (referring to specimens from the Cairngorm Mountains of Scotland), though these are misnomers as it is quartz, not topaz. The black variety is sometimes called Morion. It can often be confused with obsidian, but obsidian has a conchoidal fracture, is amorphous, and significantly less hard.

To identify smoky quartz in the field, look for its characteristic brown to black translucent color and vitreous luster. It forms well-defined hexagonal crystals, often with prism faces and rhombohedral terminations. Testing its hardness (7) will differentiate it from softer minerals. It is commonly found in Brazil, the Swiss Alps, Scotland, Madagascar, and the United States (Colorado, New Hampshire).