metamorphic
Gneiss
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 on Mohs scale; Color: Gray, black, white, and pink banding; Luster: Variable (dull to vitreous); Structure: Foliated with distinct bands (gneissose banding); Gravity: 2.6 - 2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, black, white, and pink banding
- Luster
- Variable (dull to vitreous)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, black, white, and pink banding; Luster: Variable (dull to vitreous); Structure: Foliated with distinct bands (gneissose banding); Gravity: 2.6 - 2.9.
Formation & geological history
Formed by the high-grade metamorphism of pre-existing igneous or sedimentary rocks at very high temperatures and pressures. Often found in ancient shields or core of mountain ranges.
Uses & applications
Commonly used as a dimension stone for flooring, wall facing, and decorative garden features. Also used as crushed stone for road construction and landscape aggregate.
Geological facts
Gneiss contains minerals that have been recrystallized under stress, resulting in the characteristic light and dark layers. Some of the oldest rocks on Earth, like the Acasta Gneiss (4 billion years old), are types of gneiss.
Field identification & locations
Identify by looking for distinct layers of different minerals (foliation) where the minerals are granular and visible. Often found in glaciated regions as rounded river or beach stones.
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