igneous
Weathered granite or granitic gneiss
Granite; chiefly quartz, potassium feldspar, plagioclase, and minor biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, pale gray to tan, with visible translucent quartz and feldspar; typically Mohs 6–7, nonmetallic vitreous-to-dull luster, granular interlocking crystals, and no prominent cleavage as a whole. The dark layered side may indicate weak gneissic banding or weathering.
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Physical properties
Coarse-grained, pale gray to tan, with visible translucent quartz and feldspar; typically Mohs 6–7, nonmetallic vitreous-to-dull luster, granular interlocking crystals, and no prominent cleavage as a whole. The dark layered side may indicate weak gneissic banding or weathering.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the continental crust, commonly during Precambrian to Paleozoic mountain-building; if gneissic, it was later recrystallized under high heat and pressure. Surface weathering has rounded and oxidized the specimen.
Uses & applications
Granite is widely used as crushed aggregate, building stone, countertops, monuments, and decorative slabs; small natural pieces have modest collecting value.
Geological facts
Quartz grains are usually glassy and gray, while feldspar is opaque white or pink; black grains are commonly biotite or amphibole. Granite commonly forms large plutons and continental crust.
Field identification & locations
Identify it by its visibly interlocking quartz–feldspar texture and granular break; a streak test is usually white, and it will not fizz with dilute hydrochloric acid. Common worldwide, especially in continental mountain belts and shield regions.
