igneous
Granitic Pegmatite (with Smoky Quartz and Mica)
Granitic Pegmatite (composed of SiO2, KAl2(AlSi3O10)(OH)2, and (K,Na)(AlSi3O8))
Hardness: 6-7 (Mohs scale), Color: Smoky grey, white, and dark brown/black. Luster: Vitreous to pearly. Crystal structure: Massive to coarse-grained. Cleavage: Perfect in mica flakes, none in quartz.
- Color
- Smoky grey, white, and dark brown/black
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Smoky grey, white, and dark brown/black. Luster: Vitreous to pearly. Crystal structure: Massive to coarse-grained. Cleavage: Perfect in mica flakes, none in quartz.
Formation & geological history
Formed during the final stages of a magma's crystallization, where high water content allows for the growth of very large crystals. Typically found in plutonic environments and orogenic belts.
Uses & applications
Used as a source for industrial minerals like mica, quartz, and feldspar. Occasionally used for decorative stone and specimen collecting.
Geological facts
Pegmatites are famous for containing the largest crystals ever found on Earth, with some individual crystals reaching several meters in length. This specimen shows characteristic intergrowth of smoky quartz and biotite or muscovite mica.
Field identification & locations
Identify in the field by its exceptionally coarse grain size and the presence of large plates of mica. Common in areas with exposed basement rock like the Appalachian or Rocky Mountains.
