metamorphic

Likely gneiss (banded metamorphic rock)

Felsic-to-intermediate gneiss; exact mineral identification requires closer examination

AI-generated identification · may be incorrect

Gray, coarse crystalline rock with pale, wavy mineral bands and a rough, weakly foliated surface. Likely quartz and feldspar with mica; typical Mohs hardness about 6–7, vitreous to dull luster, and no consistent cleavage as a whole rock.

Identified September 28, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when pre-existing rock was subjected to high heat and pressure, segregating minerals into bands. Gneiss commonly records deep-crustal metamorphism, often hundreds of millions to billions of years old; the photo cannot establish its age.

Uses & applications

Primarily used as crushed aggregate, dimension stone, and decorative landscaping or building stone; attractive pieces may be collected.

Geological facts

The alternating light and dark bands are called gneissic banding and distinguish many gneisses from more uniformly textured rocks.

Field identification & locations

Look for interlocking grains and mineral bands that continue across broken surfaces; a hand lens can help distinguish quartz, feldspar, and mica. The Juneau-area region is geologically diverse, so the location is compatible but not diagnostic.