metamorphic
Tumbled metamorphic pebble, likely gneiss
Foliated gneiss; commonly quartz, feldspar, mica, and amphibole
AI-generated identification · may be incorrectGray-brown, fine-to-medium grained, with subtle streaky foliation and a dull-to-slightly sparkly luster; individual crystals are poorly visible. Typical hardness is about 6–7 Mohs, with no obvious cleavage on the rounded surface and specific gravity around 2.6–2.8.
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Physical properties
Gray-brown, fine-to-medium grained, with subtle streaky foliation and a dull-to-slightly sparkly luster; individual crystals are poorly visible. Typical hardness is about 6–7 Mohs, with no obvious cleavage on the rounded surface and specific gravity around 2.6–2.8.
Formation & geological history
Gneiss forms when granite or other rocks undergoes intense heat and pressure, recrystallizing and segregating minerals into bands during regional metamorphism. Most examples formed hundreds of millions to billions of years ago in ancient continental crust.
Uses & applications
Used as crushed aggregate, dimension stone, landscaping rock, and decorative polished or tumbled stone; this small specimen is mainly suitable for collecting.
Geological facts
The elongated light-dark texture is characteristic of metamorphic foliation, though the photograph does not permit a definitive identification. It may alternatively be a weathered schist or granitic rock.
Field identification & locations
Common in metamorphic mountain belts and glacial deposits worldwide, including Scandinavia, Canada, the northeastern United States, India, and Brazil. A fresh broken surface, hand lens, streaky mineral bands, and visible mica would help confirm gneiss.
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