igneous
Pegmatitic granite with dark mafic band
Granitic pegmatite; quartz–feldspar–mica assemblage, with biotite/amphibole-rich mafic material
AI-generated identification · may be incorrectCoarse, interlocking crystals; pale quartz and feldspar with dark biotite or amphibole. Hardness is approximately 6–7 Mohs, vitreous to pearly luster, poor cleavage overall, and typical specific gravity about 2.6–2.8.
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Physical properties
Coarse, interlocking crystals; pale quartz and feldspar with dark biotite or amphibole. Hardness is approximately 6–7 Mohs, vitreous to pearly luster, poor cleavage overall, and typical specific gravity about 2.6–2.8.
Formation & geological history
Formed when silica-rich magma crystallized slowly, allowing unusually large crystals; the dark lower zone may represent a mafic enclave or compositional band. Its exact geological age cannot be determined from the photograph.
Uses & applications
Used locally as decorative stone and aggregate; attractive pieces are collected as teaching or display specimens, though this example has modest gem value.
Geological facts
The pale coarse-grained portion is characteristic of pegmatitic texture, while the fine dark portion contrasts strongly in composition and grain size.
Field identification & locations
Identify it by visible interlocking quartz, white/pink feldspar, and dark mica/amphibole, with no layering typical of sedimentary rock. Pegmatites occur worldwide, especially in granite terrains; common examples come from Maine, California, Brazil, Madagascar, and Scandinavia.
