Siltstone
“Finer than sand, coarser than clay”
Sedimentary
Siltstone is a clastic sedimentary rock made of silt-sized particles, finer than sandstone but grittier than shale. It often forms in low-energy environments like floodplains, deltas, and shallow lake beds where fine sediment settles slowly.
Composition
quartz, feldspar, clay minerals, mica
Where Found
Mississippi River Delta (USA), Ganges Delta (India), widespread in floodplain deposits globally
Mohs Hardness
6-7
Fun Fact
You can distinguish siltstone from shale by rubbing it against your teeth — siltstone feels gritty, while shale feels smooth.
Test Your Knowledge
How can you distinguish siltstone from shale in the field without equipment?
Related Specimens
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