Description
Siltstone is a sedimentary rock composed mainly of silt sized particles. It forms where water, wind, or ice deposit silt, and the silt is then compacted and cemented into a rock. Siltstone occurs in a wide range of colours. It is usually grey, brown or reddish brown. White, yellow, green, red, purple, orange, black and other colours occur. The colour is caused by the composition of the grains, the ‘composition of the cement that binds them together and stains produced by contact with subsurface waters.
Uses
Siltstone has very few uses. It is rarely the target of mining for use as a construction material or manufacturing feedstock. The intergranular pore spaces in siltstone are too small for it to serve as a good aquifer. It is rarely porous enough or extensive enough to serve as an oil or gas reservoir. Its main use is as a low-quality fill when better materials are not locally available.
Source