Tuesday, September 01, 2009
Antarcticite is a mineral form of calcium dichloride hexahydrate. It was first discovered in Don Juan Pond in Antarctica, which is probably the saltiest (47% w/v) body of water on earth. Looking at crystal structure of antarcticite (below), one can see that both name “calcium dichloride hexahydrate” and formula CaCl2·6H2O are misleading, for there are two kinds of water in it. The structure comprises the alternating layers of (i) trigonal planar triaquacalcium(2+) ions and (ii) water and chloride ions. I suppose it should be named “triaquacalcium dichloride—water (1/3)” or “triaquacalcium dichloride trihydrate”, with formula [Ca(OH2)3]Cl2·3H2O.