igneous
Quartz-rich pegmatite specimens
Granitic pegmatite; primarily quartz (SiO₂), with likely feldspar and minor mica/iron-oxide staining
AI-generated identification · may be incorrectCoarse, interlocking crystals; white to pink, tan, and rusty brown; vitreous to dull luster. Quartz hardness 7, feldspar 6–6.5, mica about 2–3; quartz lacks cleavage, while feldspar shows two cleavages. Exact mineral identification is limited by the photograph.
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Physical properties
Coarse, interlocking crystals; white to pink, tan, and rusty brown; vitreous to dull luster. Quartz hardness 7, feldspar 6–6.5, mica about 2–3; quartz lacks cleavage, while feldspar shows two cleavages. Exact mineral identification is limited by the photograph.
Formation & geological history
Pegmatites crystallize from the final, water-rich melt of granitic magma, producing unusually large crystals, commonly during Precambrian to Phanerozoic intrusive events. The reddish-brown colors likely reflect weathering and iron-oxide staining.
Uses & applications
Used as architectural and decorative stone, aggregate, silica, feldspar, and sources of rare minerals; attractive pieces are collected, though these specimens appear fairly common.
Geological facts
The large crystal size results from slow cooling and volatile-rich fluids rather than simply an exceptionally long cooling time. Pink areas are probably potassium feldspar, and translucent white areas are quartz.
Field identification & locations
Look for glassy quartz, blocky pink feldspar, and sparkly mica; a hardness test, streak, and cleavage examination can confirm them. Common worldwide in granite terrains and pegmatite districts, including Maine, California, Brazil, and Madagascar.
