metamorphic

Gneiss (likely biotite–quartz–feldspar gneiss)

Foliated gneiss; chiefly quartz (SiO₂), feldspar, biotite, and possibly amphibole

AI-generated identification · may be incorrect

Hardness about 6–7; coarse-grained, strongly banded or swirled gray, cream, brown, and black layers; vitreous quartz/feldspar luster, weak cleavage overall, and high durability. The rounded shape indicates natural water-worn or human-tumbled material.

Identified September 6, 2026More metamorphic →

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At a glance

Common name: Gneiss (likely biotite–quartz–feldspar gneiss)
Scientific name: Foliated gneiss; chiefly quartz (SiO₂), feldspar, biotite, and possibly amphibole
Category: metamorphic
Identified: September 6, 2026
Method: Standard

AI Estimated Value

About $5–$25 for a common hand specimen or landscaping piece; $30–$150 if unusually attractive, polished, or strongly patterned.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Formed when granite or other protoliths underwent high-grade regional metamorphism, typically at roughly facies conditions during mountain building; individual specimens may be Precambrian to younger. Common in continental shields and metamorphic belts.

Uses & applications

Used as crushed aggregate, dimension stone, landscaping rock, and decorative polished stone; attractive pieces are collected but usually have modest commercial value.

Geological facts

Gneissic banding results from mineral segregation and deformation under intense heat and pressure, not ordinary sedimentary layering. Dark bands commonly contain biotite or amphibole, while light bands are quartz and feldspar.

Field identification & locations

Identify it by alternating light and dark mineral bands, coarse interlocking grains, and irregular foliation; distinguish it from granite by its pronounced banding and from schist by its lower mica content and more massive texture. Common in mountain belts and glaciated terrain.