igneous
Quartz-rich pegmatite with dark mica or tourmaline
Granite pegmatite; chiefly SiO₂ quartz with feldspar and probable biotite/black tourmaline
AI-generated identification · may be incorrectCoarse, irregular translucent gray-white quartz and cream feldspar with black platy or prismatic inclusions; vitreous to pearly luster, uneven fracture, quartz hardness 7 and feldspar hardness 6–6.5. Crystal boundaries are poorly visible, but the very coarse texture is characteristic of pegmatite.
Identified More igneous →
Explore Quartz-rich pegmatite with dark mica or tourmaline in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse, irregular translucent gray-white quartz and cream feldspar with black platy or prismatic inclusions; vitreous to pearly luster, uneven fracture, quartz hardness 7 and feldspar hardness 6–6.5. Crystal boundaries are poorly visible, but the very coarse texture is characteristic of pegmatite.
Formation & geological history
Formed when silica-rich magma crystallized slowly in a late-stage dike or pocket, allowing exceptionally large crystals; typically Precambrian to Phanerozoic depending on locality. Exact identification and age require a fresh surface or testing.
Uses & applications
Mostly a collector specimen; pegmatites can supply quartz, feldspar, mica, lithium minerals, and gem tourmaline or beryl, while quartz and feldspar are used industrially.
Geological facts
Black material may be biotite mica, schorl tourmaline, or iron/manganese staining; a definitive distinction may require microscopy or chemical testing.
Field identification & locations
Common in granitic terrains worldwide, especially Brazil, Madagascar, the United States, and Scandinavia. Look for coarse interlocking crystals, glassy quartz, feldspar cleavage, and mica flakes; avoid mistaking weathered dark inclusions for ore minerals.
