igneous
Pegmatite (Granitic) with Tourmaline
Granitic Pegmatite (containing Schorl and Quartz)
Hardness: 6-7.5 (Mohs scale); Color: White to grey matrix with black inclusions; Luster: Vitreous to greasy; Crystal Structure: Large, coarse crystalline; Cleavage: Poor; Specific Gravity: 2.6-3.1
- Hardness
- 6-7
- Color
- White to grey matrix with black inclusions
- Luster
- Vitreous to greasy
Identified More igneous →
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Physical properties
Hardness: 6-7.5 (Mohs scale); Color: White to grey matrix with black inclusions; Luster: Vitreous to greasy; Crystal Structure: Large, coarse crystalline; Cleavage: Poor; Specific Gravity: 2.6-3.1
Formation & geological history
Formed during the final stages of a magma's crystallization, where high water content allows for the growth of exceptionally large crystals in intrusive igneous environments.
Uses & applications
Source of industrial minerals like quartz, feldspar, and mica; also mined for gemstones and rare earth elements.
Geological facts
Pegmatites are famous for containing the world's largest crystals, sometimes reaching several meters in length. The black inclusions seen are likely Schorl, the most common member of the tourmaline group.
Field identification & locations
Identified by the extremely coarse grain size compared to normal granite. Found in mountainous or shield regions like the Black Hills (USA), Brazil, and Madagascar. Look for large interlocking quartz and feldspar crystals.
