Solid solution in the celadonite family; the new minerals ferrosceladonite, K2Fe2+2Fe3+2Si8O20(OH)4, and ferroaluminoceladonite, K2Fe2+2Al2 Si8 O20 (OH)4

Celadonite-family mica minerals occurring in the Triassic Gavenwood Tuffs, Murihiku Supergroup, Hokonui Hills, Southland, New Zealand, have been analyzed by XRD, TEM, AEM, and EMPA. Packets a few unit cells to several hundred nanometers thick are intimately intergrown with chlorite, berthierine, and corrensite. Analyses of homogeneous packets, combined with analyses from the literature, imply complete or nearly complete solid solution between end-members of the celadonite family defined by octahedral exchange involving MgFe (super 3+) , Fe (super 2+) Al, Fe (super 2+) Fe (super 3+) , and probably MgAl, and show that EMPA analyses are commonly contaminated by mixtures. Two new minerals of the celadonite family are defined: ferroceladonite, K 2 Fe (super 2+) 2 Fe (super 3+) 2 Si 8 O 20 (OH) 4 , and ferroaluminoceladonite, K 2 Fe (super 2+) 2 Al 2 Si 8 O 20 (OH) 4 . The former occurs largely as submicrometer ( 3 . The calculated densities are 3.045 (3) and 2.928 (2) g/cm 3 for ferroceladonite and ferroaluminoceladonite, respectively. Celadonite mineral-aluminous clay mineral and celadonite mineral-Ca-rich zeolite assemblages of the zeolite facies are related to illite-chlorite+ or -pumpellyite assemblages of higher grade by dehydration reactions, not necessarily under closed-system conditions.