igneous
Granitic Pegmatite with Schorl
Granitic Pegmatite (Schorl: NaFe3Al6(Si6O18)(BO3)3(OH)3OH)
Hardness: 6-7.5 (Mohs scale); Color: White matrix (quartz/feldspar) with black inclusions (tourmaline/schorl); Luster: Vitreous to pearly; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal.
- Hardness
- 6-7
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7.5 (Mohs scale); Color: White matrix (quartz/feldspar) with black inclusions (tourmaline/schorl); Luster: Vitreous to pearly; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal.
Formation & geological history
Formed during the final stages of a magma's crystallization, where high water content allows for the growth of extremely large crystals. Typical of Proterozoic to Phanerozoic granitic intrusions.
Uses & applications
Primarily used as a source for rare elements like lithium, tantalum, and gemstones. Common specimens are used for educational purposes or architectural surfaces.
Geological facts
Pegmatites are known for containing some of the largest individual crystals ever discovered, sometimes over 10 meters long. The black inclusions are likely Schorl, the most common member of the tourmaline group.
Field identification & locations
Identify by its 'giant' grain size compared to regular granite. Usually found in mountainous regions or shield areas. Collectors should look for distinct geometric patterns and accessory minerals with vitreous luster.
