Slate
“The original chalkboard”
Metamorphic
Slate is a fine-grained metamorphic rock formed when shale or mudstone is subjected to low-grade regional metamorphism. Its signature property is perfect rock cleavage — the ability to split into thin, flat sheets along parallel planes.
Composition
quartz, muscovite, illite, chlorite
Where Found
Wales (UK), Vermont (USA), Liguria (Italy), Galicia (Spain)
Mohs Hardness
2.5-4
Fun Fact
Before paper notebooks, students wrote on small slates with chalk — the origin of the term 'clean slate.'
Test Your Knowledge
At roughly what temperature range does slate form during metamorphism?
Related Specimens
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