sedimentary
Reddish Brown Claystone or Siltstone
Argillite / Siltstone / Claystone
Hardness: 2-3 (Mohs scale), Color: Red-brown to chocolate brown, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None/Massive, Specific Gravity: 2.1-2.6
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: Red-brown to chocolate brown, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None/Massive, Specific Gravity: 2.1-2.6
Formation & geological history
Formed through the lithification of clay and silt particles deposited in low-energy environments like lake beds, river floodplains, or deep ocean basins. Often Fe-rich giving it the red-brown hue.
Uses & applications
Used largely in the brick and ceramic industry, as fill material in construction, and sometimes as a base for pigments. Fine-grained varieties are used in crafts.
Geological facts
This specimen appears water-worn or weathered into a smooth, rectangular shape. Claystones are the source of most fossils found in sedimentary layers.
Field identification & locations
Identify by its fine-grained texture (feels smooth/waxy), earthy smell when damp, and can often be scratched with a copper penny or steel knife. Found in sedimentary basins worldwide.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary