igneous
Quartz-rich pegmatite (possibly quartz–feldspar rock)
Granite pegmatite; chiefly quartz (SiO₂) with feldspar and minor mica/iron staining
AI-generated identification · may be incorrectWhite to translucent, coarse interlocking crystals with vitreous to pearly luster; quartz hardness 7, feldspar about 6, mica 2–3. No obvious cleavage in quartz, while feldspar shows blocky cleavage; low to moderate specific gravity around 2.6.
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Physical properties
White to translucent, coarse interlocking crystals with vitreous to pearly luster; quartz hardness 7, feldspar about 6, mica 2–3. No obvious cleavage in quartz, while feldspar shows blocky cleavage; low to moderate specific gravity around 2.6.
Formation & geological history
Likely formed as a late, water-rich igneous melt crystallized slowly in a granite or metamorphic host, producing unusually large crystals. Pegmatites are generally Precambrian to Phanerozoic, but the specimen’s age cannot be determined visually.
Uses & applications
Used chiefly as a collector specimen; quartz and feldspar from pegmatites are mined for glass, ceramics, abrasives, and engineered stone. Gem-quality pockets may contain tourmaline, beryl, or other gemstones.
Geological facts
The broad white, glassy masses are consistent with quartz, while tan/brown areas may be weathered feldspar or iron oxides. A definitive identification would require hardness, streak, cleavage, or testing for associated minerals.
Field identification & locations
Common in granitic terrains worldwide, including Brazil, Madagascar, India, the United States, and Scandinavia. Scratch tests and close inspection of crystal faces can distinguish quartz from feldspar; avoid acid unless carbonate minerals are suspected.
