Clay

A very fine-grained rock or mineral fragment of any composition that has a diameter of less than 0.002 mm. Moist clay is sticky and forms a ribbon when pressed between the thumb and forefinger.

Fine-grained soil or the fine-grained portion of soil that can be made to exhibit plasticity (putty-like properties) within a range of moisture contents, and that exhibits considerable strength when air-dry. Plastic soil which passes a No. 200 (0.075 mm) United States Standard sieve.