ETYM AS. claeg; akin to LG. klei, Dutch klei, and perh. to AS. clâm clay, Latin glus, gluten glue, Greek gloios glutinous substance, Eng. glue. Related to Clog.
Very fine-grained sedimentary deposit that has undergone a greater or lesser degree of consolidation. When moistened it is plastic, and it hardens on heating, which renders it impermeable. It may be white, gray, red, yellow, blue, or black, depending on its composition. Clay minerals consist largely of hydrous silicates of aluminum and magnesium together with iron, potassium, sodium, and organic substances. The crystals of clay minerals have a layered structure, capable of holding water, and are responsible for its plastic properties. According to international classification, in mechanical analysis of soil, clay has a grain size of less than 0.002 mm/0.00008 in.
Types of clay include adobe, alluvial clay, building clay, brick, cement, kaolinite, ferruginous clay, fireclay, fusible clay, puddle clay, refractory clay, and vitrifiable clay. Clays have a variety of uses, some of which, such as pottery and bricks, date back to prehistoric times.
Soil that is plastic when moist but hard when fired.