What does siltstone mean?
Siltstone is a sedimentary rock formed when loose silt, a fine sediment whose particles are smaller than sand but larger than clay, becomes compacted and cemented over time. It commonly occurs in layered formations alongside shale, mudstone, sandstone, and other sedimentary rocks. Because fine-grained sediment can preserve delicate details, siltstone may contain fossils, impressions of plant material, or other traces of ancient environments. In geology, the word distinguishes rock made chiefly from silt-sized grains from rock formed from coarser sand or finer clay. It is not usually part of everyday vocabulary, but it is useful in geology, archaeology, construction, and the study of landscapes. When describing a site informally, people may use the clearer phrase “siltstone rock,” especially if their audience is unfamiliar with the geological term.
nounA sedimentary rock composed predominantly of silt-sized particles, usually compacted and cemented into a solid rock.
- A sedimentary rock formed from compacted and cemented silt.
"The cliff exposes layers of pale siltstone shaped by centuries of erosion."
"Fossil leaves were preserved in a bed of brown siltstone."
"The construction crew encountered a layer of unstable siltstone beneath the site."
The plural is used when referring to multiple bodies or layers of siltstone.
"These siltstones preserve evidence of an ancient river environment."
Siltstone is the geological middle ground between claystone and sandstone, formed from sediment finer than sand but coarser than clay.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does siltstone come from?
The word is a compound of “silt” and “stone.” “Silt” comes from an Old English word referring to fine mud or sediment, while “stone” comes through Old English from Latin stān. The compound “siltstone” developed in English geological usage to name rock formed chiefly from silt.
How siltstone is actually used
This is primarily a geological term. In general usage, “siltstone” is uncommon, and speakers may instead say “siltstone rock” when greater clarity is needed.
Easily confused with siltstone
Siltstone is composed mainly of finer silt-sized grains, whereas sandstone consists predominantly of sand-sized grains.