metamorphic

Large rounded metamorphic boulder, likely gneiss or granitic gneiss

Gneiss (likely quartz–feldspar–mica gneiss; exact identification requires closer examination)

AI-generated identification · may be incorrect

Gray-green, coarse-grained rock with faint, wavy light and dark mineral banding and a rounded, weathered surface. Gneiss typically contains quartz, feldspar, and mica; hardness about 6–7 Mohs, vitreous to dull luster, and no prominent cleavage as a whole rock.

Identified October 13, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when pre-existing igneous or sedimentary rock was altered by high heat and pressure, producing mineral segregation or banding. The boulder’s rounded shape likely reflects prolonged weathering and transport; its age cannot be determined from the photo.

Uses & applications

Used as landscape or garden stone, retaining-wall material, and occasionally dimension stone; large boulders are mainly valued decoratively.

Geological facts

Gneissic banding forms under intense metamorphic conditions and may be folded or contorted. The visible bands are consistent with gneiss, though the photograph alone cannot confirm the rock type.

Field identification & locations

Look for alternating pale quartz/feldspar-rich and darker mica-rich bands; a fresh broken surface and hand-lens inspection help distinguish gneiss from weathered granite or other banded rocks. Gneiss occurs worldwide in ancient continental basement and mountain belts.