A platy serpentine mineral of ideal composition of Mn₂Al(Si,Al)O₅(OH)₄, and thus, the Mn²⁺ analogue of amesite. Mg and Fe²⁺ have been found to substitute for Mn and Al. Natural occurrences are rare; the type locality is Bald Knob, North Caroline, USA. Stacking disorder is common but, two-layer (2H₂) and six-layer polytypes are known to occur.
Cf., amesite, zinalsite