igneous
Pegmatitic granite, strongly weathered
Granite/pegmatite composed mainly of quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, light gray to rusty brown, with glassy quartz, pale feldspar, and reflective dark mica; hardness about 6–7 Mohs, nonfoliated, with little or no cleavage overall. Brown coloration likely comes from iron-oxide weathering of feldspar and mica.
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Physical properties
Coarse-grained, light gray to rusty brown, with glassy quartz, pale feldspar, and reflective dark mica; hardness about 6–7 Mohs, nonfoliated, with little or no cleavage overall. Brown coloration likely comes from iron-oxide weathering of feldspar and mica.
Formation & geological history
Formed when silica-rich magma crystallized slowly underground, producing unusually large crystals; pegmatites commonly formed during late stages of granitic intrusions, typically hundreds of millions to billions of years old depending on locality. Surface oxidation and weathering produced the rusty coating.
Uses & applications
Used as crushed stone, building and paving material, countertops, and an ornamental stone; attractive quartz, feldspar, or mica pockets may have modest collecting value.
Geological facts
Pegmatites can contain large crystals and rare minerals such as beryl, tourmaline, garnet, lithium minerals, or feldspar varieties. The specimen appears natural and unpolished.
Field identification & locations
Identify by interlocking visible crystals: translucent gray quartz, blocky white/pink feldspar, and platy black or silvery mica; it should scratch glass but not quartz. Common in Precambrian shields and granitic mountain regions worldwide.
