Formula: Na0.3Zn3(Si,Al)4O10(OH)2.4H2O Monoclinic
Sauconite is a zinc-rich clay mineral formed by alteration of sphalerite. It is probably widespread, but under-recognized, in the many mines of the Upper Mississippi Valley zinc-lead district.
LAFAYETTE COUNTY: Sauconite is found as “drab to pale brown soft tallow clay filling vugs in the centers of veins of sphalerite and marcasite in the Liberty Mine NE NE sec. 16 T.2N. R.1E. at Meeker’s Grove” (Heyl et al., 1959). The authors ascribe its formation to groundwater precipitation rather than in situ alteration.