metamorphic
Rounded granitic gneiss pebble
Felsic orthogneiss, composed mainly of quartz, feldspar, and mica
AI-generated identification · may be incorrectMedium- to coarse-grained, gray-green and pinkish, with a granular texture and weak foliation; quartz and feldspar give a vitreous to dull luster. Hardness is approximately 6–7 Mohs, with no prominent cleavage as a whole and a typical specific gravity near 2.6–2.8.
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Physical properties
Medium- to coarse-grained, gray-green and pinkish, with a granular texture and weak foliation; quartz and feldspar give a vitreous to dull luster. Hardness is approximately 6–7 Mohs, with no prominent cleavage as a whole and a typical specific gravity near 2.6–2.8.
Formation & geological history
Formed when granite or another felsic igneous protolith underwent high-pressure, high-temperature metamorphism, producing subtle mineral alignment; the rounded shape indicates transport by water or glacial ice. Protolith ages vary widely, commonly Precambrian to Paleozoic.
Uses & applications
Used as decorative aggregate, landscaping stone, countertops, and building stone; this water-worn specimen has modest collector value.
Geological facts
The pale grains are likely quartz and feldspar, while darker flecks are biotite or amphibole. Its subdued banding may be obscured by weathering and polishing from natural transport.
Field identification & locations
Look for interlocking crystalline grains, scattered dark mica, and faint compositional banding; it will not fizz with dilute hydrochloric acid unless carbonate veins are present. Common in streambeds, glacial deposits, and regions underlain by ancient crystalline bedrock.
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