metamorphic
Gneiss Pebble
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 (Mohs). Color: Banded layers of tan/orange feldspar, quartz, and dark biotite or hornblende. Luster: Dull to waxy when wet. Structure: Foliated with distinct mineral banding (gneissose banding).
- Hardness
- 6-7 (Mohs)
- Luster
- Dull to waxy when wet
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Physical properties
Hardness: 6-7 (Mohs). Color: Banded layers of tan/orange feldspar, quartz, and dark biotite or hornblende. Luster: Dull to waxy when wet. Structure: Foliated with distinct mineral banding (gneissose banding).
Formation & geological history
Formed through high-grade regional metamorphism of igneous or sedimentary protoliths under extreme heat and pressure, typically deep within the earth's crust during mountain-building events.
Uses & applications
Large deposits are used as crushed stone for road construction and railroad ballast. Polished specimens are used for architectural stone and landscaping decoration.
Geological facts
The banding in gneiss is caused by the separation of different mineral types during intense pressure; this specimen is a water-rounded pebble, likely smoothed by river or beach action.
Field identification & locations
Identify by looking for distinct, alternating light and dark bands (foliation). Commonly found in ancient crystalline shields or mountain ranges. This specific pebble shows oxidation staining (orange) from iron minerals.
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