sedimentary

Silty Shale or Mudstone

Siltstone/Mudstone (Clastic Sedimentary Rock)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs); Color: Dark grey, charcoal, with brown limonitic weathering; Luster: Dull or earthy; Structure: Fine-grained, fissile or blocky; Cleavage: Parallel to bedding planes.

Hardness: 3-4 (Mohs)
Color: Dark grey, charcoal, with brown limonitic weathering
Luster: Dull or earthy

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs); Color: Dark grey, charcoal, with brown limonitic weathering; Luster: Dull or earthy; Structure: Fine-grained, fissile or blocky; Cleavage: Parallel to bedding planes.

Formation & geological history

Formed through the lithification of silt and clay particles deposited in low-energy environments such as river floodplains, lagoons, or deep marine basins. These rocks can date from any geological era depending on the deposit location.

Uses & applications

Primarily used in the manufacture of cement, brick making, and crushed stone for road construction. Some organic-rich shales are sources of natural gas or oil.

Geological facts

Shales account for over 50% of all sedimentary rocks found on the Earth's surface. They are excellent for preserving fossils due to the fine grain size which can capture intricate details of organisms.

Field identification & locations

Identify by its fine-grained texture, tendency to split into thin sheets (fissility), and muddy smell when wet. Commonly found in riverbeds and coastal cliffs. Collectors should look for signs of fossil impressions along bedding planes.