Here's why:
* Clay-rich: Shale is primarily composed of clay minerals, which are very fine-grained.
* Compression: The layers of clay are compressed over time due to the weight of overlying sediments. This process squeezes out water and compacts the material.
* Dark color: Shale often has a dark gray to black color due to the presence of organic matter, which is common in clay-rich sediments.
Other characteristics of shale:
* Fissile: Shale has a tendency to split into thin layers or flakes.
* Fine-grained: Shale is characterized by its very small grain size, which is typically less than 0.0625 mm (1/16 mm).
* Sedimentary: It is a sedimentary rock, formed from the accumulation and lithification of sediment.
Let me know if you have any more questions!
