igneous
Quartz-bearing pegmatite
Quartz (SiO₂) with feldspar and mica, likely a granitic pegmatite
AI-generated identification · may be incorrectCoarse, interlocking translucent white to smoky quartz crystals with tan feldspar and possible mica; quartz hardness 7, vitreous luster, no cleavage, hexagonal crystal structure. The specimen is irregular and partly weathered, so exact mineral proportions are uncertain.
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Physical properties
Coarse, interlocking translucent white to smoky quartz crystals with tan feldspar and possible mica; quartz hardness 7, vitreous luster, no cleavage, hexagonal crystal structure. The specimen is irregular and partly weathered, so exact mineral proportions are uncertain.
Formation & geological history
Formed when silica-rich magma crystallized slowly in a late-stage pegmatite vein, allowing unusually large crystals to grow. Pegmatites are generally Precambrian to Phanerozoic and occur in or near granitic intrusions.
Uses & applications
Used as a teaching and display specimen; quartz and feldspar from pegmatites can be sources of industrial silica, ceramics, and glass. Attractive crystals may be sold to collectors, though this example appears moderately aesthetic rather than gem quality.
Geological facts
Pegmatites commonly contain large quartz, feldspar, and mica crystals and may host tourmaline, beryl, lithium minerals, or rare earth minerals.
Field identification & locations
Identify by the very coarse texture, glassy quartz, blocky feldspar, and flaky mica; unlike glass, quartz feels cold and scratches steel. Common worldwide in granitic terrains, including Brazil, the United States, Madagascar, and Scandinavia.
