metamorphic

Coarse-grained metamorphic rock, likely gneiss

Biotite–quartz–feldspar gneiss (probable; exact identification requires a fresh surface and tests)

AI-generated identification · may be incorrect

Hardness about 6–7; dark gray to black with white, tan, and rusty minerals, weakly banded/foliated texture, and vitreous to dull luster. Likely quartz, feldspar, and biotite or hornblende; no obvious cleavage is visible at specimen scale.

Identified September 3, 2026More metamorphic →

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At a glance

Common name: Coarse-grained metamorphic rock, likely gneiss
Scientific name: Biotite–quartz–feldspar gneiss (probable; exact identification requires a fresh surface and tests)
Category: metamorphic
Identified: September 3, 2026
Method: Standard

AI Estimated Value

About $5–$30 as an unexceptional hand specimen; roughly $30–$100 if unusually attractive, labeled, or polished.

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 preexisting granite or sedimentary rock underwent high-grade heat and pressure, producing mineral segregation and foliation, commonly during Precambrian to Paleozoic mountain-building events.

Uses & applications

Used as dimension stone, paving, wall stone, aggregate, and landscaping material; attractive polished pieces may be decorative, but this specimen appears ordinary rather than gem-grade.

Geological facts

The photograph suggests gneiss but could also represent weathered granite, diorite, or amphibolite; visible color zoning alone is insufficient for confident classification.

Field identification & locations

Look for alternating light quartz-feldspar and dark mica/amphibole bands, granular interlocking crystals, and a nonporous, heavy feel; a streak, hardness, and fresh fracture test would help. Common worldwide in ancient continental shields and mountain belts.