igneous
Quartz-rich pegmatite with drusy quartz
Quartz (SiO₂) in a granitic pegmatite, likely with feldspar and mica inclusions
AI-generated identification · may be incorrectGray to brown, translucent crystalline matrix with a sparkling cavity of small quartz crystals; vitreous luster, Mohs hardness about 7 for quartz, poor cleavage, and specific gravity near 2.65. The rough outer surface and intergrown crystals are characteristic of a natural rock specimen.
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Physical properties
Gray to brown, translucent crystalline matrix with a sparkling cavity of small quartz crystals; vitreous luster, Mohs hardness about 7 for quartz, poor cleavage, and specific gravity near 2.65. The rough outer surface and intergrown crystals are characteristic of a natural rock specimen.
Formation & geological history
Likely formed from the final, volatile-rich melt of a granitic intrusion, where quartz and feldspar crystals grew slowly in cavities. Pegmatites are generally Precambrian to Phanerozoic, depending on locality, but the exact age cannot be determined from the image.
Uses & applications
Used mainly as a collector specimen, décor, and occasionally for lapidary work; quartz from pegmatites is also important industrially. This piece is probably not suitable for high-grade jewelry cutting.
Geological facts
The sparkly cavity is drusy quartz—many tiny crystals coating a surface—while the brown coloration may reflect iron staining or weathering. Individual quartz crystals can show six-sided prisms and pyramidal terminations.
Field identification & locations
Look for glassy luster, scratch resistance against ordinary steel, and visible quartz crystals; acid testing is unnecessary. Common sources include Brazil, Madagascar, the United States, and other granitic regions.
