argillite

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argillite

[′är·jə‚līt]
(petrology)
A compact rock formed from siltstone, shale, or claystone but intermediate in degree of induration and structure between them and slate; argillite is more indurated than mudstone but lacks the fissility of shale.

argillite

A rock containing chiefly clay materials; derived from claystone, siltstone, or shale; used locally as building stone, although rarely produced commercially.