igneous
Coarse-grained Quartz and Feldspar Pegmatite
Pegmatite (Quartz: SiO2, Feldspar: KAlSi3O8)
Hardness: 6-7 on Mohs scale; Color: white to off-white crystals with darker host rock; Luster: Vitreous (glassy) to earthy; Crystal Structure: Trigonal (Quartz) and Monoclinic (Feldspar); Massive texture with large visible interlocking crystals.
- Hardness
- 6-7 on Mohs scale
- Color
- white to off-white crystals with darker host rock
- Luster
- Vitreous (glassy) to earthy
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: white to off-white crystals with darker host rock; Luster: Vitreous (glassy) to earthy; Crystal Structure: Trigonal (Quartz) and Monoclinic (Feldspar); Massive texture with large visible interlocking crystals.
Formation & geological history
Formed during the final stages of a magma body's crystallization. Highly concentrated water-rich fluids allow large crystals to grow rapidly at depth. Usually associated with granitic batholiths from the Phanerozoic to Precambrian eras.
Uses & applications
Quartz and Feldspar are used in glass and ceramic manufacturing. High-purity quartz is used in electronic components and silicon production. Collectors value unique mineral associations within pegmatite veins.
Geological facts
Pegmatite is famous for containing the world's largest crystals, some reaching over 10 meters in length. They are the primary source of many gemstones like tourmaline, beryl, and topaz.
Field identification & locations
Identify in the field by looking for unusually large, interlocking crystals of quartz and feldspar within granitic terrain. Check for the lack of bubbles and high hardness (cannot be scratched by steel). Usually found in mountain belts and shield areas like the Appalachians or the Rockies.
