igneous
Quartz-rich pegmatitic rock, possibly altered granite
Quartz–feldspar pegmatite; probable composition of quartz (SiO₂), feldspar, and mica/secondary alteration minerals
AI-generated identification · may be incorrectCoarse, irregular white to tan grains with glassy quartz, chalky/weathered feldspar, and dark mica or other accessory minerals; quartz hardness 7, feldspar about 6, nonmetallic luster, no obvious cleavage in quartz. Exact identification is limited by weathering and the single photograph.
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Physical properties
Coarse, irregular white to tan grains with glassy quartz, chalky/weathered feldspar, and dark mica or other accessory minerals; quartz hardness 7, feldspar about 6, nonmetallic luster, no obvious cleavage in quartz. Exact identification is limited by weathering and the single photograph.
Formation & geological history
Likely crystallized slowly from silica-rich magma in a granite-related vein or intrusion, allowing large crystals to grow; commonly Precambrian to younger, depending on locality. Surface weathering has altered feldspar and possibly iron-bearing minerals.
Uses & applications
Pegmatites are sources of quartz, feldspar, mica, lithium, beryl, and tourmaline; attractive pieces may be collected, while this weathered fragment has little commercial use.
Geological facts
The pale, sugary texture and large interlocking grains are typical of pegmatitic or highly coarse granite material. Dark specks may be biotite, amphibole, iron oxides, or sulfide minerals.
Field identification & locations
Look for very coarse interlocking crystals, translucent gray-white quartz, blocky feldspar cleavage, and mica flakes; a streak, hardness, cleavage, and acid test would improve identification. Common in granite and metamorphic terranes worldwide.
