sedimentary

Argillite

Argillite (compacted clay- and silt-sized mineral particles)

AI-generated identification · may be incorrect

Hardness of 3 to 4 on the Mohs scale, typically reddish-brown to dark gray in color, with a dull to earthy luster and massive or very fine-grained crystal structure.

Identified November 5, 2026More sedimentary →

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Physical properties

Hardness of 3 to 4 on the Mohs scale, typically reddish-brown to dark gray in color, with a dull to earthy luster and massive or very fine-grained crystal structure.

Formation & geological history

Formed through the compaction and lithification of fine-grained argillaceous sediments like clay and silt over millions of years in marine or lacustrine environments.

Uses & applications

Used primarily in carving decorative items, traditional Indigenous art (such as Haida argillite carvings), and occasionally as a low-grade fill material.

Geological facts

Argillite is an intermediate rock type between shale and slate, lacking the strong foliation characteristic of true slates.

Field identification & locations

Identified by its fine-grained texture, lack of fissility compared to shale, and softness that allows it to be easily scratched with a knife or nail. Found worldwide in sedimentary basins.