igneous
Quartz-rich pegmatite fragment
Milky quartz with feldspar and mica; primarily SiO₂, with K-feldspar/plagioclase and muscovite
AI-generated identification · may be incorrectCoarse, interlocking crystals with translucent white-gray quartz, cream feldspar, and reflective mica; vitreous to pearly luster. Quartz hardness is 7, feldspar 6–6.5, mica 2–3; quartz lacks cleavage, while feldspar shows two cleavages.
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Physical properties
Coarse, interlocking crystals with translucent white-gray quartz, cream feldspar, and reflective mica; vitreous to pearly luster. Quartz hardness is 7, feldspar 6–6.5, mica 2–3; quartz lacks cleavage, while feldspar shows two cleavages.
Formation & geological history
Likely crystallized slowly from water-rich magma in a granitic pegmatite, producing unusually large crystals. Pegmatites are generally Precambrian to Phanerozoic, depending on locality; exact age cannot be determined from the image.
Uses & applications
Commonly collected as a cabinet specimen; quartz and feldspar are industrial minerals, while attractive pegmatite may be used decoratively. This piece appears too fractured and irregular for jewelry.
Geological facts
The translucent, glassy areas are probably quartz, and the platy reflective surfaces are likely mica. Acid testing is usually ineffective because quartz and feldspar do not fizz.
Field identification & locations
Identify by its very coarse texture, glassy quartz, blocky feldspar cleavage, and flaky mica; common in granitic terrains worldwide, including Brazil, Madagascar, the United States, and Canada.
