igneous
Mica-rich pegmatite fragment
Muscovite–quartz–feldspar pegmatite; commonly contains KAl₂(AlSi₃O₁₀)(OH)₂ muscovite
AI-generated identification · may be incorrectHardness is about 2–2.5 for muscovite and 6–7 for quartz; pale silvery, gray, and brown with a sparkling vitreous-to-pearly luster. Coarse interlocking crystals and perfect basal cleavage in mica produce the obvious flaky reflective surfaces.
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Physical properties
Hardness is about 2–2.5 for muscovite and 6–7 for quartz; pale silvery, gray, and brown with a sparkling vitreous-to-pearly luster. Coarse interlocking crystals and perfect basal cleavage in mica produce the obvious flaky reflective surfaces.
Formation & geological history
Formed from the final, volatile-rich melt of a slowly cooling granitic intrusion, allowing exceptionally large crystals; typically Mesozoic to Precambrian depending on locality. The exact age cannot be determined from the photograph.
Uses & applications
Usually collected as a mineral specimen; pegmatites are important sources of feldspar, quartz, mica, lithium, beryl, and tantalum. Attractive mica-rich pieces may be used decoratively but this fragment has modest commercial value.
Geological facts
The bright sheets are likely muscovite mica, while translucent granular areas may be quartz or feldspar. Mica can split into flexible, transparent sheets along one perfect cleavage plane.
Field identification & locations
Common in granitic pegmatites worldwide, including Brazil, India, Madagascar, the United States, and Scandinavia. Test by peeling or scratching the silvery flakes; quartz remains hard and scratches glass, whereas mica does not.
