igneous
Mica-bearing pegmatite
Granitic pegmatite composed mainly of quartz, feldspar, and biotite/muscovite mica
AI-generated identification · may be incorrectCoarse-grained, irregular specimen with reflective black-to-silvery mica flakes, translucent pale feldspar or quartz, and brown weathering. Quartz hardness is 7, feldspar 6–6.5, and mica 2–3; luster is glassy to pearly with sheet-like cleavage in mica.
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Physical properties
Coarse-grained, irregular specimen with reflective black-to-silvery mica flakes, translucent pale feldspar or quartz, and brown weathering. Quartz hardness is 7, feldspar 6–6.5, and mica 2–3; luster is glassy to pearly with sheet-like cleavage in mica.
Formation & geological history
Formed when water-rich granitic magma cooled slowly in a late-stage dike or vein, allowing unusually large crystals to grow. Pegmatites are generally Precambrian to younger and occur in continental crust near granite intrusions.
Uses & applications
Used as an ornamental and teaching specimen; pegmatites can be sources of feldspar, quartz, mica, lithium, beryllium, and rare minerals, though this small piece has little commercial value.
Geological facts
The dark reflective flakes are likely biotite, while pale transparent areas may be quartz or feldspar. Exact identification would require testing or magnification because the photograph does not resolve individual crystals clearly.
Field identification & locations
Look for exceptionally coarse interlocking crystals, mica sheets that split elastically, and glassy quartz without cleavage. Common localities include Brazil, Madagascar, the United States, and other granitic regions.
