metamorphic

Rounded granitic gneiss pebble

Biotite-rich granitoid gneiss; quartz + feldspar + biotite, with minor accessory minerals

AI-generated identification · may be incorrect

Hardness about 6–7 Mohs; brown-gray, coarse-grained, granular texture with weak foliation and possible quartz/feldspar veins; vitreous to dull luster, no obvious cleavage as a whole, specific gravity roughly 2.6–2.8.

Identified September 4, 2026More metamorphic →

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Physical properties

Formation & geological history

Likely metamorphosed granite formed deep in the continental crust during an ancient mountain-building event, then uplifted, weathered, and rounded by water or glacial transport; exact age cannot be determined from the photograph.

Uses & applications

Commonly used as aggregate, riprap, landscaping stone, and sometimes dimension stone; attractive polished pieces may be sold as display specimens, but this example appears mainly collectible as a natural pebble.

Geological facts

The light grains are probably quartz and feldspar, while dark flakes are likely biotite or amphibole. Stronger mineral banding or recrystallized texture would support gneiss rather than ordinary granite.

Field identification & locations

Identify it by its interlocking crystalline grains, hardness, dark mica-like specks, and subtle mineral alignment; common in eroded mountain belts and glacial or river gravels worldwide. A streak test, hand lens, and acid test can help distinguish it from similar rocks.