igneous
Quartz-rich pegmatite
Granitic pegmatite, chiefly quartz (SiO₂) with feldspar and possible mica
AI-generated identification · may be incorrectCoarse-grained, white to gray, with vitreous quartz and possibly pearly mica; quartz hardness 7, feldspar about 6, mica 2–3. Irregular fracture dominates quartz, while feldspar may show cleavage; density commonly 2.6–2.7 g/cm³.
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Physical properties
Coarse-grained, white to gray, with vitreous quartz and possibly pearly mica; quartz hardness 7, feldspar about 6, mica 2–3. Irregular fracture dominates quartz, while feldspar may show cleavage; density commonly 2.6–2.7 g/cm³.
Formation & geological history
Formed when water-rich, silica-rich magma crystallized slowly in a late-stage igneous vein or pocket, producing unusually large crystals. Most pegmatites formed during Precambrian to Phanerozoic mountain-building events, depending on locality.
Uses & applications
Used as a source of quartz, feldspar, mica, lithium, and rare elements; attractive pieces are collected, though this specimen appears moderately common and not gem-grade.
Geological facts
The image shows a strongly weathered, coarse aggregate rather than a single crystal. Dark patches may be biotite, hornblende, or iron-stained fractures; exact identification requires testing or a fresh broken surface.
Field identification & locations
Common in granitic terrains worldwide, including Maine, California, Brazil, Madagascar, and Scandinavia. Look for very coarse interlocking crystals, a glassy quartz response, and feldspar cleavage; a streak test and hardness test help distinguish it from calcite or soft altered rock.
