igneous
Quartz-rich pegmatite specimen
Pegmatite composed mainly of quartz (SiO₂), feldspar, and mica, with possible tourmaline or garnet inclusions
AI-generated identification · may be incorrectCoarse, irregular interlocking crystals; translucent gray-white quartz, cream feldspar, and dark accessory minerals with vitreous to pearly luster. Quartz hardness is 7, feldspar about 6, and mica 2–3; cleavage is prominent in feldspar and mica but absent in quartz.
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Physical properties
Coarse, irregular interlocking crystals; translucent gray-white quartz, cream feldspar, and dark accessory minerals with vitreous to pearly luster. Quartz hardness is 7, feldspar about 6, and mica 2–3; cleavage is prominent in feldspar and mica but absent in quartz.
Formation & geological history
Formed when water-rich granitic magma cooled slowly in a late-stage vein or pocket, allowing exceptionally large crystals to grow. Pegmatites formed throughout geological history, commonly during Precambrian to Mesozoic granite emplacement.
Uses & applications
Used as a source of quartz, feldspar, mica, lithium, and rare-element minerals; attractive pieces are collected as mineral specimens. Gem-quality pockets may yield tourmaline, beryl, garnet, or topaz.
Geological facts
The very coarse texture is the defining feature of pegmatite. Dark brown to black grains may be schorl tourmaline, biotite, or garnet, but photographs alone cannot confirm the accessory minerals.
Field identification & locations
Common in granite terrains and exposed pegmatite dikes, especially in Brazil, Madagascar, the United States, and Scandinavia. Look for unusually large interlocking quartz and feldspar crystals and test suspected quartz for glass-scratching hardness.
