igneous
Quartz-bearing feldspathic pegmatite
Pegmatite, chiefly quartz (SiO₂) and potassium feldspar (KAlSi₃O₈), possibly with mica
AI-generated identification · may be incorrectCoarse-grained, pale pink to cream rock with glassy to pearly crystals and irregular cavities lined by quartz or feldspar; quartz hardness 7, feldspar 6–6.5, nonmetallic luster, generally poor cleavage overall but feldspar has two cleavages. Exact mineral identification is limited by the image.
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Physical properties
Coarse-grained, pale pink to cream rock with glassy to pearly crystals and irregular cavities lined by quartz or feldspar; quartz hardness 7, feldspar 6–6.5, nonmetallic luster, generally poor cleavage overall but feldspar has two cleavages. Exact mineral identification is limited by the image.
Formation & geological history
Forms when the final, water-rich melt from a cooling granitic magma crystallizes slowly in veins or pockets, producing exceptionally large crystals. Pegmatites are commonly Precambrian to Phanerozoic, depending on the host intrusion.
Uses & applications
Used as a source of feldspar, quartz, mica, lithium, and rare-element minerals; attractive specimens are sold for collecting and occasionally cut or polished as ornamental stone.
Geological facts
Open cavities called miarolitic vugs may contain late-stage quartz, feldspar, mica, or tourmaline crystals. The pink coloration commonly reflects iron-bearing potassium feldspar.
Field identification & locations
Look for extremely coarse interlocking crystals, blocky pink feldspar, glassy gray-white quartz, and possible mica flakes; common in granitic terrains worldwide, including Brazil, Madagascar, the United States, and Canada.
