01 / Origin story
How does siltstone form?
Siltstone is a clastic sedimentary rock made of particles between sand and clay in size (silt) — deposited in slower-moving water than sandstone's sand, but more energetic than shale's still water.
02 / Read the clues
How can you identify siltstone?
Use several clues together.
One photograph shows one specimen, not every variation.
03 / Commonly confused with
Similar at first glance.
Compare the materials side by side.
Photographs are not shown to the same scale.
Siltstone ↗
Fine-grained, but with a slight gritty feel — finer than sandstone, coarser than shale
Shale ↗
Very fine-grained, smooth to the touch
Sandstone ↗
Visibly grainy texture, feels gritty
04 / Out in the world
Where it’s found.
River floodplains, lake margins — environments with moderate water energy.
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