igneous
Quartz-rich pegmatite with red feldspar or garnet inclusions
Granitoid pegmatite; chiefly quartz and feldspar, with possible almandine garnet or iron-oxide inclusions
AI-generated identification · may be incorrectTypically Mohs 6–7, pale gray to white, with a vitreous quartz luster and blocky feldspar grains; the red grains may be garnet (Mohs 6.5–7.5) or altered feldspar. Massive, coarse-grained texture; cleavage is absent in quartz but good in feldspar.
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Physical properties
Typically Mohs 6–7, pale gray to white, with a vitreous quartz luster and blocky feldspar grains; the red grains may be garnet (Mohs 6.5–7.5) or altered feldspar. Massive, coarse-grained texture; cleavage is absent in quartz but good in feldspar.
Formation & geological history
Likely crystallized slowly from a silica-rich magma in a deep igneous intrusion, allowing large crystals to grow. Pegmatites are commonly Precambrian to Mesozoic, though the specimen’s age cannot be determined from the image.
Uses & applications
Used mainly as a collector specimen; similar pegmatites provide quartz, feldspar, mica, and gemstones, while massive varieties may be used decoratively or as aggregate.
Geological facts
The colorful inclusions and very coarse texture are characteristic of pegmatitic rocks. A streak, hardness, and close inspection of crystal faces would help distinguish garnet from red feldspar or iron staining.
Field identification & locations
Common in granitic terrains and famous districts such as Maine, South Dakota, Brazil, and Madagascar. Look for interlocking oversized crystals, glassy quartz, feldspar cleavage, and garnet’s lack of cleavage.
