igneous
Mica-bearing quartz rock (likely pegmatite)
Quartz–feldspar–mica pegmatite; dark mica is probably biotite, possibly muscovite or chlorite
AI-generated identification · may be incorrectCoarse-grained, pale gray to white quartz and feldspar with platy, reflective dark mica; quartz hardness 7, feldspar 6–6.5, biotite 2.5–3, with vitreous to pearly luster. The specimen shows interlocking crystals and mica cleavage, but exact identification requires testing.
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Physical properties
Coarse-grained, pale gray to white quartz and feldspar with platy, reflective dark mica; quartz hardness 7, feldspar 6–6.5, biotite 2.5–3, with vitreous to pearly luster. The specimen shows interlocking crystals and mica cleavage, but exact identification requires testing.
Formation & geological history
Likely formed from the final, volatile-rich melt of a granitic intrusion, producing exceptionally large crystals during slow cooling, typically in Precambrian to Phanerozoic continental crust. Common in pegmatite dikes and granite-associated veins.
Uses & applications
Used mainly as a collector specimen; pegmatites may also supply feldspar, quartz, mica, lithium, beryllium, and rare-element minerals. This example has limited jewelry or construction value unless it contains gem-quality crystals.
Geological facts
The dark mineral’s shiny flakes and excellent basal cleavage are characteristic of mica. A glassy quartz fracture and feldspar cleavage help distinguish this rock from ordinary granite.
Field identification & locations
Common in pegmatite districts worldwide, including Brazil, Madagascar, the United States, Canada, and Scandinavia. Inspect for large crystal faces, mica sheets, and possible accessory minerals; a streak, hardness, and microscope test would refine identification.
