- Definition and Composition
- Shale is a fine-grained sedimentary rock containing clay minerals and quartz
- Typical composition includes 58% clay minerals, 28% quartz, and 6% feldspar
- Contains about 95% of organic matter in sedimentary rocks
- Typically gray in color, with variations from red to black
- Formation and Deposition
- Most shales are marine in origin and form in slow-moving water
- Clay particles form aggregates and floccules due to slow settling
- Deposited in lakes, river deltas, floodplains, and offshore basins
- Forms through diagenesis process with compaction and lithification
- Properties and Uses
- Shows fissility, breaking into thin layers less than 1 cm thick
- Acts as semipermeable medium, allowing water passage while retaining salts
- Contains fossils, animal tracks, and raindrop impressions
- Most common source rock for hydrocarbons (natural gas and petroleum)
- Historical Context
- Term "shale" was used interchangeably with slate until mid-19th century
- Black shale associated with coal mining called "black metal"