igneous
Quartz–feldspar–mica pegmatite
Granitic pegmatite, composed chiefly of quartz (SiO₂), feldspar, and dark mica (biotite); possibly containing tourmaline or amphibole
AI-generated identification · may be incorrectCoarse, irregular interlocking crystals; translucent gray-white quartz, pale feldspar, and black platy or prismatic minerals with vitreous to pearly luster. Quartz hardness is 7 Mohs, feldspar 6–6.5, and biotite 2.5–3; feldspar commonly shows cleavage.
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Physical properties
Coarse, irregular interlocking crystals; translucent gray-white quartz, pale feldspar, and black platy or prismatic minerals with vitreous to pearly luster. Quartz hardness is 7 Mohs, feldspar 6–6.5, and biotite 2.5–3; feldspar commonly shows cleavage.
Formation & geological history
Formed when water-rich, silica-rich magma cooled slowly in veins or pockets, allowing exceptionally large crystals to grow, typically during Precambrian to Mesozoic intrusive events. The exact locality and age cannot be determined from the image.
Uses & applications
Used as an ornamental and educational specimen; pegmatites are important sources of quartz, feldspar, mica, lithium minerals, beryl, and tourmaline, while attractive crystals may be collected as mineral specimens.
Geological facts
The specimen appears to be a rough, weathered aggregate rather than a single crystal. Dark areas could be biotite, schorl tourmaline, or amphibole, so a definitive identification requires testing or magnification.
Field identification & locations
Look for very coarse crystals, quartz’s lack of cleavage, feldspar cleavage, and mica’s sheet-like splitting; common in granitic terrains and pegmatite districts worldwide. Typical rough hand specimen value is about $5–$30 USD, rising to $50–$200+ if rare, well-crystallized minerals are confirmed.
