Mudstone

About it

Smooth, fine-grained rock of hardened clay and silt that breaks into blocks rather than splitting into thin sheets like shale. One of the commonest sedimentary rocks, and often fossil-bearing.

Type

Rock (sedimentary)

Group

Sedimentary (clastic)

Lustre

dull, earthy

Colours

grey, black, red, brown, green

Transparency

opaque

Cleavage and fracture

blocky, not splitting into thin layers

Typical values: real specimens vary. For more, see mindat.org.