igneous
Quartz–feldspar pegmatite fragment
Granite-family pegmatite, chiefly quartz (SiO₂) and feldspar, with minor mica or sulfide inclusions
AI-generated identification · may be incorrectCoarse, interlocking crystals; translucent white to gray quartz with cream/white blocky feldspar and possible dark mica. Quartz hardness 7, feldspar 6–6.5; vitreous to pearly luster, no cleavage in quartz, two cleavages in feldspar; typical specific gravity 2.6–2.7.
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Physical properties
Coarse, interlocking crystals; translucent white to gray quartz with cream/white blocky feldspar and possible dark mica. Quartz hardness 7, feldspar 6–6.5; vitreous to pearly luster, no cleavage in quartz, two cleavages in feldspar; typical specific gravity 2.6–2.7.
Formation & geological history
Slow cooling of silica-rich magma in a vein or pocket produced the unusually large crystals, generally during Precambrian to Phanerozoic intrusive activity. The dark metallic grain may be mica, galena, or another accessory mineral and cannot be identified confidently from the photo.
Uses & applications
Commonly collected as a mineral specimen; similar pegmatites provide feldspar, quartz, mica, lithium, and rare-element ores. Attractive pieces may be used decoratively, but this small fragment has little commercial use.
Geological facts
Pegmatites are famous for exceptionally large crystals and can host tourmaline, beryl, garnet, and lithium minerals. A streak, hardness, cleavage, and fresh break would help identify the dark inclusion.
Field identification & locations
Common in granitic terrains worldwide, including Maine, California, Brazil, Madagascar, and Norway. Look for coarse crystals, glassy quartz, and feldspar cleavage; avoid assuming the specimen is a gemstone without testing.
