A common sedimentary
rock produced from clay, which has a fine-grained
structure in well-defined narrow strata, 0.1–0.4 mm (0.004–0.016
in.) thick, each representing a period of deposition. Shales are rich in
fossils, and may contain carbonaceous matter
and oil. Their metamorphism produces slate.
| Shale. Credit: Mineral Information
AND PLANETARY SCIENCE