Three groups: (1) Cn(BaAl 2 Si 2 O 8 )-poor, Ab-rich ones containing unmixed albite phases, (2) Cn-rich varieties showing occasional unmixed celsian phases and (3) those with Cn contents intermediate between those of the first two groups. The compositions of the unmixed phases in the second group are Cn 54 Or 34 Ab 12 and Cn 95 Or 5 . Almost all contain considerable amounts of Fe (super 3+) which probably replaces Al (super 3+) . As a result, their lattice dimensions are slightly larger than those of other (Ba,K)-feldspars.--Modified journal abstract.

You do not currently have access to this article.