igneous
Feldspar-rich Pegmatite
Granitic Pegmatite (principally KAlSi3O8)
Hardness: 6-6.5 (Mohs scale); Color: Pinkish-tan to brownish-orange; Luster: Vitreous to pearly; Crystal structure: Monoclinic/Triclinic; Cleavage: Two directions at nearly 90 degrees; Specific gravity: 2.5–2.6.
- Hardness
- 6-6
- Color
- Pinkish-tan to brownish-orange
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-6.5 (Mohs scale); Color: Pinkish-tan to brownish-orange; Luster: Vitreous to pearly; Crystal structure: Monoclinic/Triclinic; Cleavage: Two directions at nearly 90 degrees; Specific gravity: 2.5–2.6.
Formation & geological history
Formed through the slow cooling of water-rich magma in the final stages of a granitic intrusion’s crystallization. This allows for the growth of very large crystals. These rocks can be found in terrains ranging from Precambrian to Cenozoic ages.
Uses & applications
Used in the manufacture of glass and ceramics (pottery, porcelain, tiles). It is also a source of semi-precious gemstones (such as moonstone or sunstone) and rare-earth minerals in larger deposits.
Geological facts
Feldspars make up about 60% of the Earth's crust. Granitic pegmatites are unique because they often contain rare elements like lithium, tantalum, and niobium which are not found in ordinary granite.
Field identification & locations
Identify in the field by its coarse crystal size (typically >1cm), blocky cleavage planes that reflect light, and typical pink/orange hue. Common in plutonic mountainous regions. Collectors look for well-formed crystal faces.
