492 



A. J. JjTpses — 3£in era logical J\ T otes. 



This means a mineral of closely the type of felsobanyite 

 (2A1„0 3 . SO 3 +10H„O), for the ratio yields (H„ 8 Ca 10 Al 4 )O 30 (SO 3 ) 6 

 +40H 2 O or 2R 2 3 . S0 3 + 8H 2 0. This formula not only suits 

 the analysis of the Arizona mineral almost exactly but that of 

 the Ettringen variety at least as well as the formula assumed 

 as may be seen. 









Percentages 



Percentages 









required by 



required by 





Ettringite of 



Ettringite of 



(H 26 Ca 10 Al 4 )'O 30 



6CaO, Alo0 3 , 3SO 





Ettringen. 



Arizona. 



(8O,) s + 40H a O. 



32HoO. 



CaO. 



_.. 27-27 



26-31 



26-21 



26-4 



Al s O, 



.. 7-76 



9-72 



9-55 



8-0 



so 3 . 



... 19-15 



18-54 



18-72 



18-9 



H.O. 



... 45-82 



45-41 



45-50 



46-7 



We may therefore conclude that this mineral is to be placed 

 in a group of hydrous basic sulphates of the general formula 

 2R 2 3 . S0 3 +nH„0 and that the definite and close division be- 

 tween the loss at 115° and at red heat in my analysis supports 

 the supposition that 14 pts. of H 2 may be considered as basic 

 in the Arizona variety while the almost perfect agreement in 

 total H 2 in the Arizona and Ettringen analyses makes a sim- 

 ilar assertion for the latter not improbable. 



The calculated ratio would yield the formula for the Arizona 

 variety 



H 28 Ca 10 Al 4 O 30 .5SO 3 + 40H 2 O 



While the assumed formula for the Ettringen variety might 

 be written 



H 18 Ca 6 Al 5 18 .3S0 3 + 24H 2 



Both of these are of the type 2R 2 3 . S0 3 -HiH 2 and 

 closely agree when reduced 



Arizona variety 2[H JJ CaAl 8 3 ] . S0 3 +8H 2 



5 5 



Ettringen variety . 2[H 3 CaAl i 3 J . S0 3 + 8H<,0 



s 



T The group therefore of hydrous basic sulphates of the gene- 

 ral formula 2R„0 3 . S0 3 + ?iH 2 is composed of 



Glockerite 2Fe 2 3 . S0 3 + 6H 2 Earthy or massive. 



Felsobanyite 2AL 2 3 . S0 3 + lOHoO Ortborhornbic six sided scales. 



Paraluminite 2AL,0 3 . S0 3 + 15H 2 Massive. 



f Arizona _ 2[H 14 0aAlgO 3 ].SO 3 + 8H 2 Silky double refracting fibers. 



Ettringite . Kttringen 2[H 3 CaAL0 3 ]. S0 3 + 8H 2 Hexagonal needle crystals. 

 Mineralogical Laboratory, Columbia College. 



