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Related Clues:
- Crystalline, flaky rock
- Say nothing, given drink that may be full of gas!
- Rock that's 'fracked'
- Oil-yielding mineral
- Rock from which slate is formed
- Easily cleaved rock
- Oil source has excited the French
- Product of clay compaction
- Introduction of secure, healthy, source of gas
- Oil source has damaged the French
- Some mudrock
- Frackable rock
- Rock formed from clay
- Earth's crust, mostly
- Rock in which fossils can be found