igneous
Pegmatite with Schorl (Black Tourmaline) and Mica
Pegmatite (complex association of NaAlSi3O8, NaFe3Al6(BO3)3Si6O18(OH)4, and KAl2(AlSi3O10)(OH,F)2)
Hardness: 6-7.5 (depending on mineral); Color: White/off-white matrix with black prismatic crystals and green/pink mica flakes; Luster: Vitreous to pearly; Crystal structure: Orthorhombic/Trigonal; Specific gravity: 2.6-3.2
- Hardness
- 6-7
- Luster
- Vitreous to pearly
Identified More igneous →
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Physical properties
Hardness: 6-7.5 (depending on mineral); Color: White/off-white matrix with black prismatic crystals and green/pink mica flakes; Luster: Vitreous to pearly; Crystal structure: Orthorhombic/Trigonal; Specific gravity: 2.6-3.2
Formation & geological history
Formed during the final stages of a magma chamber's crystallization. The high water and volatile content allows for the growth of exceptionally large crystals in intrusive igneous environments.
Uses & applications
Used primarily as mineral specimens for collectors; granite-like varieties are used in construction, while specific minerals within (like tourmaline) may be used as gemstones if of high quality.
Geological facts
Pegmatites are known as 'nature's treasure chest' because they can contain giant crystals; some black tourmaline crystals in pegmatites have been recorded at several meters long.
Field identification & locations
Identify by finding very large, coarse-grained crystals embedded in a lighter feldspar or quartz matrix. Commonly found in mountainous regions with historical tectonic activity, such as the Appalachian or Rocky Mountains.
