igneous
Quartz-rich pegmatite (likely feldspar–quartz rock)
Granitic pegmatite; chiefly quartz (SiO₂) and feldspar, with possible mica/iron-oxide staining
AI-generated identification · may be incorrectCoarse, irregular interlocking crystals; white to cream quartz/feldspar with rusty-brown iron-oxide staining and small cavities. Quartz hardness is 7 Mohs with vitreous luster; feldspar is 6–6.5, commonly showing cleavage. Exact mineral proportions cannot be confirmed from the image.
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Physical properties
Coarse, irregular interlocking crystals; white to cream quartz/feldspar with rusty-brown iron-oxide staining and small cavities. Quartz hardness is 7 Mohs with vitreous luster; feldspar is 6–6.5, commonly showing cleavage. Exact mineral proportions cannot be confirmed from the image.
Formation & geological history
Likely formed as a late-stage, volatile-rich igneous melt cooled slowly in a granitic intrusion, producing exceptionally large crystals; commonly Precambrian to younger, depending on locality. Brown areas likely reflect weathering and oxidation of iron-bearing minerals.
Uses & applications
Used mainly as a decorative or collector specimen; quartz and feldspar from pegmatites are industrially important for glass, ceramics, and electronics, though this irregular piece is unlikely to have commercial value.
Geological facts
Pegmatites can host spectacular crystals of tourmaline, beryl, spodumene, and rare-element minerals. Cavities may contain drusy quartz or secondary minerals.
Field identification & locations
Look for very coarse grains, glassy quartz, blocky feldspar cleavage, and mica flakes; a hardness or acid test and fresh break would help distinguish it from weathered quartzite or granite. Common in granitic terrains worldwide, including Brazil, Madagascar, the United States, and India.
