Slate
Rock made of quartz, illite, chlorite
Common
The finest-grained foliated rock: shale or volcanic ash lightly metamorphosed so that it splits into smooth, thin sheets. North Wales slate comes in every grey, and purple, green and blue.
Rock
- Kind of rock
- Metamorphic rock
- Rock family
- Schist and gneiss
- Texture
- foliated (splits along its layers), fine-grained
- Also contains
- Mica, Feldspar
- How it forms
- Low-grade regional metamorphism compresses clay-rich rock, and new flakes of mica and chlorite grow across the squeeze (slaty cleavage).
- Uses
- Roofing tiles, floor tiles, billiard tables and writing slates.
Crystallography
- Habits
- Foliated
Physical properties
- Luster
- Dull, Silky
- Colors
- gray, dark gray, purple, green
- Transparency
- Opaque
Geology
- Origins
- Metamorphic
- Geography
- Wales (North Wales), USA (New York, Pennsylvania, Virginia), Brazil
Classification
- Rarity
- Common
- Gem quality
- No
Sources
- Slate. Wikipedia.
- S. Robertson, BGS Rock Classification Scheme, Volume 2: Classification of metamorphic rocks (Research Report RR 99-02). British Geological Survey, 1999.
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