igneous
Quartz–feldspar pegmatite fragment
Granitic pegmatite; chiefly quartz (SiO₂) and feldspar, with possible mica/amphibole
AI-generated identification · may be incorrectCoarse, interlocking crystals; pale gray-white quartz/feldspar with darker mica or amphibole. Quartz has Mohs hardness 7 and vitreous luster; feldspar is hardness 6–6.5 with two cleavage directions. Exact mineral identification is limited by the photo.
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Physical properties
Coarse, interlocking crystals; pale gray-white quartz/feldspar with darker mica or amphibole. Quartz has Mohs hardness 7 and vitreous luster; feldspar is hardness 6–6.5 with two cleavage directions. Exact mineral identification is limited by the photo.
Formation & geological history
Forms when the final, water-rich melt from a granitic magma crystallizes slowly in veins or pockets, commonly during the Precambrian to Phanerozoic. The dark host appears to be a fine-grained volcanic or metamorphic rock.
Uses & applications
Used as a source of feldspar, quartz, mica, and occasionally lithium or rare-metal minerals; attractive specimens are collected, while ordinary pieces have little industrial or jewelry value.
Geological facts
Pegmatites can contain exceptionally large crystals and gemstones such as tourmaline, beryl, topaz, and spodumene. The specimen’s granular texture and contrasting dark matrix are characteristic of a vein or intrusive fragment.
Field identification & locations
Look for very large crystals, glassy quartz, blocky feldspar cleavage, and flaky mica; acid testing is unnecessary. Common in granitic terrains worldwide, especially Brazil, the United States, Canada, and Madagascar.
