metamorphic
Gneissic Schist
Foliated Metamorphic Rock (Schist/Gneiss transition)
Hardness: 6-7 (Mohs scale); Color: Gray, white, and black banded; Luster: Dull to sub-vitreous with sparkling mica flakes; Crystal Structure: Foliated with visible mineral alignment; Cleavage: Good along foliation planes; Specific Gravity: 2.7-2.9
- Hardness
- 6-7 (Mohs scale)
- Color
- Gray, white, and black banded
- Luster
- Dull to sub-vitreous with sparkling mica flakes
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Gray, white, and black banded; Luster: Dull to sub-vitreous with sparkling mica flakes; Crystal Structure: Foliated with visible mineral alignment; Cleavage: Good along foliation planes; Specific Gravity: 2.7-2.9
Formation & geological history
Formed through high-grade regional metamorphism of clay-rich sedimentary rocks (shale) or igneous rocks (granite) at high temperatures and pressures. Most common in Precambrian shields or mountain roots.
Uses & applications
Used primarily as decorative stone, crushed stone for construction, road fill, and occasionally as garden landscaping material. High-quality slabs may be used for flooring or countertops.
Geological facts
The foliation in this rock represents the direction of pressure applied during its formation deep within the Earth's crust. Schists are often more than a billion years old in certain continental shields.
Field identification & locations
Identify in the field by looking for distinct layers (foliation) and the presence of shiny mica minerals like muscovite or biotite. It is ubiquitous in mountainous terrains like the Appalachians or Alps.
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