1. . 
Solid particles of size less than 2 microns equivalent spherical diameter, also identified as clay by definitions in International Standards Organization ISO/CD 13501, par. 3.1.17. Because of extremely small size, these solids largely defy direct removal by mechanical devices that rely on screening or gravitational forces. Their removal is aided by chemical aggregation prior to gravity separation or filtration.
See: acrylamide polymer, acrylamide acrylate polymer, acrylate polymer, Bingham plastic model, clay extender, clay-water interaction, clear-water drilling, closed mud system, colloid, dispersion, dispersion, fines, gel, gelled-up mud, gumbo, native-solids mud, plastic viscosity, prehydrated bentonite, reserve-mud pit, siderite, silicate mud, smectite clay, wastewater cleanup, water clarification