igneous
Pegmatitic granite (quartz–feldspar–mica rock)
Granitic pegmatite; mainly quartz (SiO₂), feldspars, and biotite/muscovite mica
AI-generated identification · may be incorrectCoarse-grained, light gray to cream with orange-brown weathered feldspar and black mica; vitreous quartz, pearly mica, and blocky feldspar crystals. Hardness is about 6–7 overall; quartz has no cleavage, feldspar has two cleavages, and mica has perfect basal cleavage.
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Physical properties
Coarse-grained, light gray to cream with orange-brown weathered feldspar and black mica; vitreous quartz, pearly mica, and blocky feldspar crystals. Hardness is about 6–7 overall; quartz has no cleavage, feldspar has two cleavages, and mica has perfect basal cleavage.
Formation & geological history
Formed when water-rich granitic magma cooled slowly in a late-stage intrusive dike or pocket, allowing exceptionally large crystals to grow. Most pegmatites formed during Precambrian or younger continental igneous events.
Uses & applications
Used as dimension stone, countertops, aggregate, and decorative material; associated pegmatites may yield feldspar, quartz, mica, tourmaline, beryl, or lithium minerals. This modest polished slice is primarily a teaching or ornamental specimen.
Geological facts
The specimen’s rounded polished face and coarse interlocking crystals strongly indicate a cut and polished sample. Dark flakes are likely biotite, while translucent gray-white areas are quartz.
Field identification & locations
Identify it by large visible interlocking crystals, glassy quartz, cleavage-bearing feldspar, and flaky mica; granite generally does not fizz with dilute hydrochloric acid. Common worldwide in continental mountain belts and pegmatite districts.
