metamorphic
Gneiss
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 (Mohs scale), Color: Banded grey, white, and pink, Luster: Dull to vitreous, Structure: Foliated with distinct bands (gneissose banding), Cleavage: Poor, but splits along bands.
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Banded grey, white, and pink, Luster: Dull to vitreous, Structure: Foliated with distinct bands (gneissose banding), Cleavage: Poor, but splits along bands.
Formation & geological history
Formed under high temperature and high pressure conditions (regional metamorphism) from pre-existing igneous or sedimentary rocks. This sample shows a distinct quartz/feldspar vein cross-cutting the foliation.
Uses & applications
Used as crushed stone for road construction, building stone, and decorative landscaping. High-quality specimens are used for countertops.
Geological facts
Gneiss makes up some of the oldest bedrock on Earth, such as the Acasta Gneiss in Canada, which is over 4 billion years old.
Field identification & locations
Identified by 'ribbons' or bands of alternating light and dark minerals. Found in the roots of mountain ranges and ancient continental shields. Look for visible crystalline structures within the bands.
