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Hardened sedimentary rock that is composed primarily of angular silt-sized particles (seesilt) and that is not laminated or easily split into thin layers. Siltstones, which are hard and durable, occur in thin layers rarely thick enough to be classified as formations. They are intermediate between sandstones and shales but are not as common as either.
This entry comes from Encyclopædia Britannica Concise. For the full entry on siltstone, visit Britannica.com.