Gneiss

Coarse-grained, gray rock with visible light and dark mineral grains and weak foliation; likely quartz, feldspar, and mica or amphibole. Typical hardness is about 6–7 Mohs; crystals are interlocking, with no single cleavage.

Forms when pre-existing igneous or sedimentary rocks undergo high-grade heat and pressure, commonly deep in continental crust. Gneisses range from ancient Precambrian rocks to younger regional metamorphic belts; the image alone cannot establish its age.

Used as dimension stone, landscaping rock, aggregate, and occasionally for countertops or decorative stone.

Gneiss is identified by mineral segregation or banding, though some specimens—like this one—show subdued banding rather than strong stripes.

Look for coarse, interlocking grains and alternating pale quartz/feldspar and darker mica or amphibole; common in ancient continental shields and mountain belts. Exact identification requires closer inspection, as several coarse metamorphic rocks can look similar.