sedimentary

Argillite

Argillite (compact, clay-rich sedimentary rock)

AI-generated identification · may be incorrect

Hardness of 3-4 on the Mohs scale, grayish-green or dark gray color, dull luster, very fine-grained microcrystalline structure, poor to moderate cleavage, specific gravity around 2.5-2.7

Identified July 31, 2026More sedimentary →

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Physical properties

Hardness of 3-4 on the Mohs scale, grayish-green or dark gray color, dull luster, very fine-grained microcrystalline structure, poor to moderate cleavage, specific gravity around 2.5-2.7

Formation & geological history

Formed through the lithification of mud, clay, and silt over millions of years, typically in quiet marine or lacustrine depositional environments.

Uses & applications

Used historically by indigenous peoples for carving tools and ceremonial items (such as Haida argillite carvings), and locally for decorative landscaping or crushed stone.

Geological facts

Argillite is an intermediate rock type between shale and slate, lacking the strong slaty cleavage of true slate but harder and more cemented than standard shale.

Field identification & locations

Found in sedimentary strata worldwide; can be identified in the field by its fine-grained texture, lack of fissility typical of shale, and relative softness compared to slate.