igneous
Quartz-rich pegmatite fragment
Granitic pegmatite, chiefly quartz (SiO₂) with feldspar and mica
AI-generated identification · may be incorrectCoarse interlocking crystals with glassy to pearly luster; translucent gray-white quartz, pale feldspar, and dark mica. Quartz hardness is 7 Mohs; feldspar 6–6.5 and mica 2–3, with uneven fracture and variable cleavage; typical specific gravity about 2.6–2.8.
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Physical properties
Coarse interlocking crystals with glassy to pearly luster; translucent gray-white quartz, pale feldspar, and dark mica. Quartz hardness is 7 Mohs; feldspar 6–6.5 and mica 2–3, with uneven fracture and variable cleavage; typical specific gravity about 2.6–2.8.
Formation & geological history
Formed when water-rich granitic magma cooled slowly in a late-stage intrusive dike, allowing unusually large crystals to grow. Most pegmatites formed during Precambrian to Mesozoic plutonic activity, depending on locality.
Uses & applications
Commonly collected as a mineral specimen; larger, cleaner pegmatites may provide feldspar, quartz, mica, lithium, and rare-element ores, but this small fragment has negligible commercial value.
Geological facts
The granular sparkle likely comes from quartz and mica cleavage surfaces rather than metallic ore. Pegmatites are important sources of tourmaline, beryl, spodumene, and other gem minerals.
Field identification & locations
Identify by very coarse grain size, interlocking quartz-feldspar crystals, and flaky dark mica; a steel file will not scratch quartz, while mica flakes easily. Common in granite terrains worldwide, including Maine, California, Brazil, Madagascar, and Norway.
