sedimentary

Argillite / Mudstone

Argillaceous sedimentary rock

Hardness: 2-3 on the Mohs scale. Color: Purplish-red to brownish-red due to iron oxide. Luster: Dull or earthy. Crystal structure: Microcrystalline, composed of clay-sized particles and quartz silt. Cleavage: Poor to moderately well-developed parallel to bedding planes. Specific gravity: 2.2-2.6.

Hardness: 2-3 on the Mohs scale
Color: Purplish-red to brownish-red due to iron oxide
Luster: Dull or earthy

Identified August 6, 2026More sedimentary →

Explore Argillite / Mudstone in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the compaction and lithification of mud, silt, and clay particles accumulated in quiet aquatic environments such as lake bottoms, river floodplains, or marine basins. Geological age varies widely from Precambrian to recent.

Uses & applications

Used primarily in brick and tile manufacturing, cement production, and occasionally carved into ornamental items or pipes by indigenous cultures.

Geological facts

The reddish-purple coloration is characteristic of hematite (iron oxide) acting as a pigment and cementing agent in an oxidizing depositional environment.

Field identification & locations

Found worldwide in sedimentary basins. Identified by its very fine-grained texture, earthy appearance, and lack of visible mineral grains without magnification.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Quartz pebble

Silicon dioxide (SiO2)

sedimentary

Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

sedimentary

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary