sedimentary

Shale (Ferruginous)

Laminated Mudrock (Siliciclastic Sedimentary Rock)

Hardness: 3-4 (Mohs scale); Color: Dark brown to black (iron-stained); Luster: Dull/Earthy; Crystal Structure: Clastic fine-grained; Cleavage: Fissile (splits into thin layers); Specific Gravity: 2.4-2.8

Hardness: 3-4 (Mohs scale)
Color: Dark brown to black (iron-stained)
Luster: Dull/Earthy

Identified May 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the lithification of mud and clay particles deposited in slow-moving water environments like lake beds or deep ocean floors. The brownish hue indicates presence of iron oxides (hematite or goethite).

Uses & applications

Used in the production of bricks, cement, and ceramics. Some oil-rich shales are processed for natural gas or petroleum (fracking).

Geological facts

Shale is the most common sedimentary rock on Earth, making up an estimated 70% of the sedimentary rocks in the crust. Many shales preserve fossils incredibly well due to their fine-grained nature.

Field identification & locations

Identify by its ability to split into thin sheets (fissility) and its soft, fine-textured surface. Commonly found in river basins and near ancient seafloors. It usually produces a 'clink' sound when tapped with a hammer.

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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