metamorphic
Gneiss
Metamorphic Gneiss
Hardness: 6-7 on Mohs scale. Color: Tan, brown, greenish-gray, and orange-iron staining. Luster: Dull to sub-vitreous. Structure: Foliated with distinct compositional banding. Cleavage: Poor to none, breaks unevenly.
- Hardness
- 6-7 on Mohs scale
- Color
- Tan, brown, greenish-gray, and orange-iron staining
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Tan, brown, greenish-gray, and orange-iron staining. Luster: Dull to sub-vitreous. Structure: Foliated with distinct compositional banding. Cleavage: Poor to none, breaks unevenly.
Formation & geological history
Formed under high-grade regional metamorphism (high temperature and pressure) acting on pre-existing igneous or sedimentary rocks like granite or shale. The location (~69.9°N, 23.2°E in Northern Norway) is part of the Baltic Shield and Caledonian Orogenic Belt, rich in Precambrian metamorphic rocks.
Uses & applications
Widely used as crushed stone for construction, aggregate, road base, and dimension stone for paving or building facades.
Geological facts
Gneiss is one of the oldest rock types found on Earth, with some specimens in Northern Europe and Canada dating back over 3.5 to 4 billion years. Its name originates from an old German mining term meaning 'spark' or 'bright'.
Field identification & locations
Identified by light and dark parallel mineral bands or foliation. Highly characteristic of Fennoscandian metamorphic terranes. Look for alternating quartz/feldspar and biotite/amphibole layers.
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