In geotechnical engineering, high-activity clays have activities that range from about >1 to 7+, with smectitic clays (i.e., smectite or interstratifications with a smectite-like component) being the most common having activities near 3 (where Ca-saturated, or in high salinity environments) to 7+ (where Na-dominated and at low salinity).
See activity, clay; low-activity clays; quick clays