sedimentary

Shale (with minor calcite veining)

Clastic sedimentary rock (primarily clay minerals and quartz)

Hardness: 3 on Mohs scale; Color: Dark grey to charcoal black; Luster: Dull/Earthy; Crystal structure: Non-crystalline/fine-grained; Cleavage: Fissile (splits along planes); Specific gravity: 2.4 - 2.8

Hardness: 3 on Mohs scale
Color: Dark grey to charcoal black
Luster: Dull/Earthy

Identified March 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the compaction and lithification of silt and clay-sized mineral particles ('mud'). Often found in ancient lake beds, floodplains, or marine environments. Geological age can range from Precambrian to Holocene.

Uses & applications

Primary source for natural gas (fracking) and petroleum. Crushed shale is used in road construction, brick making, and the production of Portland cement.

Geological facts

Black shales are rich in organic matter and represent some of the world's most significant energy reserves. They often preserve delicate fossils, such as trilobites or leaves, because of the low-energy water environment they form in.

Field identification & locations

Identify in the field by its tendency to break into thin, flat, brittle flakes (fissility). It will not fizz with acid unless it has calcite veins like this specimen. Found globally in sedimentary basins.

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