Extremely fine particles, less than 0.002mm across forming constituent components of natural and anthropogenic sediments and deposits. The plastic raw material from which pottery, daub, bricks, and other forms of terracotta are made comprising mainly clay-sized particles of the principal clay minerals kaolinite, illite, and montmorillonite. Potting clay is a relatively abundant and widespread resource, although the quality and characteristics of different outcrops vary greatly, the best being highly sought-after.