igneous
Smoky Quartz and Feldspar Pegmatite
Granitic Pegmatite (chiefly SiO2 and KAlSi3O8)
Hardness: 6-7 (Mohs scale); Color: Grayish-black smoky quartz with tan/white feldspar and iron staining; Luster: Vitreous (glassy) to dull; Crystal structure: Hexagonal (quartz) and Monoclinic (feldspar); Specific gravity: ~2.6-2.7
- Hardness
- 6-7 (Mohs scale)
- Luster
- Vitreous (glassy) to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Grayish-black smoky quartz with tan/white feldspar and iron staining; Luster: Vitreous (glassy) to dull; Crystal structure: Hexagonal (quartz) and Monoclinic (feldspar); Specific gravity: ~2.6-2.7
Formation & geological history
Formed during the final stages of a magma's crystallization, where high water content allows for the growth of large crystals in veins or dikes. Common in Precambrian or Paleozoic geological environments.
Uses & applications
Used primarily for mineral collecting; quartz can be used in glassmaking and feldspar in ceramics. High-quality smoky quartz is used in jewelry.
Geological facts
Pegmatites are famous for containing the largest crystals found on Earth. The dark 'smoky' color in the quartz crystals is often the result of natural irradiation of silicon dioxide crystals over millions of years.
Field identification & locations
Identify by looking for very large, interlocking crystalline grains (quartz, feldspar, mica) in a vein-like structure. Commonly found in mountainous regions with exposed granite basements.
