Interstratified biotite-chlorite (mixed layers: 1 biotite layer - x chlorite layers); "x" commonly = 1 (1:1 regular interstratification), but can range from 1 to 4.
(NB: The "biotite" and "chlorite" layers could each be composed of several different species, and the number of chlorite layers is not defined, so, theoretically, this group term could be applied to several tens of different phases.)
(TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.