igneous
Quartz-bearing feldspar pegmatite (likely with mica/tourmaline)
Granitic pegmatite; chiefly quartz (SiO₂) and feldspar, with dark mica or tourmaline
AI-generated identification · may be incorrectCoarse interlocking crystals; translucent white quartz, creamy feldspar, and black flaky or prismatic accessory minerals. Quartz hardness 7, feldspar 6–6.5, mica 2–3; glassy to pearly luster, with feldspar cleavage and quartz lacking cleavage.
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Physical properties
Coarse interlocking crystals; translucent white quartz, creamy feldspar, and black flaky or prismatic accessory minerals. Quartz hardness 7, feldspar 6–6.5, mica 2–3; glassy to pearly luster, with feldspar cleavage and quartz lacking cleavage.
Formation & geological history
Formed when volatile-rich granitic magma crystallized slowly in a late-stage dike or pocket, producing unusually large crystals. Pegmatites are generally Precambrian to Phanerozoic and commonly intrude older continental crust.
Uses & applications
Used as a source of feldspar, quartz, mica, lithium, and rare-element minerals; attractive pieces are collected, while gem-quality varieties may contain tourmaline, beryl, or topaz.
Geological facts
The specimen visibly shows a coarse, sugary white matrix with dark inclusions and honey-colored translucent material, consistent with pegmatite rather than a single mineral.
Field identification & locations
Common in granitic and metamorphic terrains, including Maine, California, Colorado, Brazil, Madagascar, and Afghanistan. Identify it by its exceptionally coarse texture, mixed minerals, and blocky feldspar cleavage; a definitive ID requires testing or microscopy.
