Siltstone is a fine to medium-grained sedimentary rock. It is pale grey or brown and quite soft. Sometimes it contains thin layers which are darker or lighter in colour.
Siltstones are made up of particles which are intermediate in size between sandstone and mudstone.
How is it formed?
Siltstones are formed by particles settling through water and accumulating on the ocean floor, river beds or lagoon and lake bottoms. As the silt is buried and compacted by overlying sediment, the water is squeezed out and it turns into siltstone.