TF. T. Schaller — The Alunite-Beudantite Group. 363 



free from CO a , although these latter contain more water than 

 is usual. Perhaps the line grinding of the samples has a* very 

 marked effect on the water content of these minerals, as 

 Hartley has suggested for pharmacosiderite. 



The mineral harttite is an isomorphous mixture of about two 

 parts of hamlinite and one part of a strontium alunite. More 

 accurately the ratio is 1*97 to 1 instead of exactly 2 to 1. Its 

 formula may therefore be written 2[2Sr0.3Al 2 3 '.2P 2 5 .7H 2 0] 

 + l[Sr0.3Al 2 3 .4S0 3 .6H 2 0], which can be simplified " to 

 5SrO.9Al 2 O 3 .4P 2 O 6 .4SO 3 .20H 2 O. This is very close to the 

 formula deduced by Hussak, whose formula, quadrupled, gives: 

 4SrO.8Al 2 O 3 .4P 2 O 6 .4SO 3 .20H 2 O. In fact, the ratios deduced 

 by Hussak from the analysis of harttite are in better agree- 

 ment with the formula here proposed than his own. 



Batios of Harttite. 







Required by 



Required by 







Hussak's 



Schaller's 





Ratios of analysis 



formula 



formula 



SrO 



1664 457 



4-00 

 8-00 

 4-00 

 4 00 



5-00 



Al 



3355 9-22 



9-00 



PO 



1528 4-20 



4-00 



sa 6 



1475 4-05 



4-00 



H.O 



1733 19-60 



20-00 



20-00 



The Minerals of the group. 



The minerals forming the aluuite-beudantite group may be 

 divided into three smaller groups, — the sulphates, the phos- 

 phates, and the sulphate-phosphates. Taking alunite as the 

 type of the sulphates, hamlinite of the phosphates, and corkite 

 as that of the sulphate-phosphates, we have : 



Alunite K 2 0. 3A1 2 3 . 4S0 3 . 6H 2 0. 



Hamlinite 2SrO. 3A1 2 8 . 2P 2 6 . 7H 2 0. 



Corkite., 2PbO. 3Fe 3 8 . 2S0 3 .P 2 6 . 6H 2 0. 



The analogous composition is not clearly seen in the three 

 formulas just given, but it is possible, by rewriting them in 

 a slightly different form, to show very clearly the analogy 

 between them : 



Alunite K 2 0. 3A1 2 3 . 6H 2 0. 2SO s . 2SO s . 



Hamlinite SrO. 3A1 2 3 . 6H 2 0. 2HP0 3 . Sr(P0 3 ) 2 . 



Corkite PbO. 3Fe 2 3 . 6H a O. 2S0 3 . Pb(P0 3 ) 2 . 



By assuming the isomorphous replacement of S0 3 by HP0 3 , 

 the relationship becomes very clear. The formulas can, how- 

 ever, be better written by regarding =[SOJ and = [HPOJ as 



