Mudstone

“Earth's quiet record keeper”

Sedimentary

Mudstone is a fine-grained sedimentary rock made of clay and silt that, unlike shale, does not split into thin layers. It forms in calm, low-energy environments and frequently preserves exquisite fossils because the fine sediment captures delicate details.

Composition

clay minerals, quartz, feldspar, calcite, organic matter

Where Found

Burgess Shale region (Canada), Green River Formation (USA), widespread in river and lake deposits globally

Mohs Hardness

2-3

Fun Fact

Some of the best-preserved dinosaur skin impressions ever found were encased in mudstone, capturing texture details down to individual scales.