igneous
Biotite-rich granite or granodiorite
Coarse-grained plutonic rock, likely granodiorite; composed mainly of quartz, plagioclase feldspar, potassium feldspar, and dark biotite/hornblende.
AI-generated identification · may be incorrectGray, speckled, granular texture with abundant dark mica; crystalline and nonfoliated, with uneven fracture and little/no cleavage as a whole. Typical hardness is about 6–7 Mohs and specific gravity approximately 2.65–2.75.
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Physical properties
Gray, speckled, granular texture with abundant dark mica; crystalline and nonfoliated, with uneven fracture and little/no cleavage as a whole. Typical hardness is about 6–7 Mohs and specific gravity approximately 2.65–2.75.
Formation & geological history
Formed when silica-rich magma cooled slowly deep within Earth, allowing visible crystals to grow; commonly Paleozoic to Precambrian in exposed continental crust, though age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, building stone, paving, and monuments; an ordinary hand specimen has minimal commercial value.
Geological facts
The dark flakes are likely biotite or hornblende, while pale grains are feldspar and quartz. Its apparent layering may reflect weathering or an irregular fracture rather than true metamorphic foliation.
Field identification & locations
Identify it by its interlocking visible crystals, gray color, hardness, and lack of vesicles or sedimentary layering; a streak test is usually white, and quartz grains should resist scratching with steel. Common worldwide in mountain batholiths and continental shields.
