1. a fine-grained sedimentary rock formed from clay or silt that has been hardened but not metamorphosed
Usage: geological

Examples

• The geologist identified the dark gray rock as argillite.
• Argillite formations are common in ancient lake beds.
• The quarry produced high-quality argillite for construction.
• Native American artisans carved intricate designs into the soft argillite.
• The cliff face revealed layers of argillite deposited millions of years ago.
• Argillite weathers more easily than harder metamorphic rocks.