metamorphic

Rounded granitic gneiss or granitoid boulder

Biotite-bearing orthogneiss; chiefly quartz, feldspar, and biotite

AI-generated identification · may be incorrect

Coarse-grained, gray-green, faintly banded, and strongly rounded; likely Mohs 6–7, with vitreous quartz and dull feldspar. No obvious cleavage as a whole rock; density commonly 2.6–2.8 g/cm³.

Identified August 15, 2026More metamorphic →

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At a glance

Common name: Rounded granitic gneiss or granitoid boulder
Scientific name: Biotite-bearing orthogneiss; chiefly quartz, feldspar, and biotite
Category: metamorphic
Identified: August 15, 2026
Method: Standard

AI Estimated Value

Typically $20–$150 as a landscaping boulder; uncommon, attractive specimens may bring $100–$500 to collectors, depending mainly on size and provenance.

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

Coarse-grained, gray-green, faintly banded, and strongly rounded; likely Mohs 6–7, with vitreous quartz and dull feldspar. No obvious cleavage as a whole rock; density commonly 2.6–2.8 g/cm³.

Formation & geological history

Probably an ancient continental crustal rock metamorphosed and later rounded by glacial, river, or coastal transport. Exact age and classification require a fresh surface, thin section, or geochemical analysis.

Uses & applications

Used as landscape stone, garden boulders, riprap, and occasionally dimension stone or aggregate; generally not a jewelry material.

Geological facts

The elongated dark and light streaks may represent gneissic foliation, while the smooth shape indicates prolonged abrasion. Weathering has produced the muted green-gray surface.

Field identification & locations

Common in glaciated and mountainous regions, including parts of New England, the Canadian Shield, Scandinavia, and the Rocky Mountains. Look for quartz and feldspar grains, dark biotite, and planar mineral alignment; a magnet test may detect minor magnetite.