sedimentary
Mudstone
Argillite
Hardness: 2-3 (Mohs scale), Color: Dark brown or grey, Luster: Dull or earthy, Crystal structure: Clastic (microscopic), Cleavage: None (unlike shale, it doesn't split into thin layers), Specific Gravity: 2.4-2.8
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 2-3 (Mohs scale), Color: Dark brown or grey, Luster: Dull or earthy, Crystal structure: Clastic (microscopic), Cleavage: None (unlike shale, it doesn't split into thin layers), Specific Gravity: 2.4-2.8
Formation & geological history
Formed from the lithification of suspended silt and clay-sized particles in quiet water environments like lakes, lagoons, or deep oceans. Age varies significantly across geological epochs.
Uses & applications
Primarily used as fill material in construction, crushed stone for road bases, and sometimes in the manufacturing of cement and bricks.
Geological facts
Mudstone is the most common type of sedimentary rock on Earth. While it looks like a simple rock, it often contains microscopic fossils and helps geologists reconstruct ancient aquatic environments.
Field identification & locations
Identify in the field by its fine grain and lack of visible crystals. It will often feel smooth to the touch and can sometimes be scratched with a penny. Commonly found in riverbeds, cliffsides, and areas with ancient lake beds.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary