metamorphic

Gneiss (specifically a Granitic Gneiss specimen)

Gneiss (high-grade metamorphic rock primarily composed of Quartz, Feldspar, and Biotite/Amphibole)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Pinkish-orange, tan, and dark grey/black bands; Luster: Vitreous to dull; Structure: Gneissic banding (foliated); Specific Gravity: 2.6-2.9.

Hardness: 6-7 on Mohs scale
Color: Pinkish-orange, tan, and dark grey/black bands
Luster: Vitreous to dull

Identified February 18, 2026More metamorphic →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Pinkish-orange, tan, and dark grey/black bands; Luster: Vitreous to dull; Structure: Gneissic banding (foliated); Specific Gravity: 2.6-2.9.

Formation & geological history

Formed via high-grade regional metamorphism of granite or sedimentary protoliths under intense heat and pressure. Commonly dates back to the Precambrian or Paleozoic eras within deep crustal environments.

Uses & applications

Used primarily as crushed stone for road construction, landscaping boulders, and occasionally as architectural facing or dimension stone (granite-like countertops).

Geological facts

Gneiss contains some of the oldest known rocks on Earth, such as the Acasta Gneiss in Canada which is over 4 billion years old. The 'eyes' or lens-shaped minerals sometimes found in it are called porphyroblasts.

Field identification & locations

Identify by looking for distinct 'segregation' bands where light minerals (quartz/feldspar) and dark minerals (biotite/hornblende) separate. This smooth, water-worn cobble shape suggests it was found in a riverbed or glacial deposit. Common in mountainous regions like the Appalachians or Canadian Shield.