Chlorine in vesuvianites

Vesuvianites with high contents of chlorine near 1 apfu occur in the rodingite-like rocksof the Wiluy River, Sakha-Yakutia, Russia — the type locality for grossular and wiluite. Chlorine isincorporated into the vesuvianite structure at the O(10) site substituting O, OH or F. The classification ofvesuvianite-group minerals is discussed on the basis of available structural data from Cl- and F-bearingvesuvianites. A ternary O-F(+Cl)-OH diagram (hypothetical “oxyvesuvianite” — fluorvesuvianite — hypothetical“hydroxylvesuvianite”) is proposed for distinguishing fluorvesuvianite. A rule of 50% Cl anda boundary content of 0.5 apfu of Cl are proposed for distinguishing “chlorvesuvianite”.