Eakle.] 



Mineralogical Notes. 



323 



taste is strongly astringent and the water obtained in a closed tube 

 is strongly acid. The mineral is soluble in water, and when the 

 solution is heated, a precipitate of red sesquioxide of iron is 

 formed. It is easily and completely soluble in dilute acids. 

 Two analyses of the mineral gave as its composition : — 









Mean analysis 







Per cent. 



Per cent. 



Per cent. 



Ratio. 



Fe 2 O s 



12.95 



I303 



12.99 



.812 



A1A 



7-3° 



7.58 



7-44 



.729 



so 3 



38.44 



37-63 



3804 



4-755 



H 2 at 1 io° C. 



23-32 



24-13 



23.72 



13-179 1 



H.,0, ignition 



13.40 



14.02 



i3-7i 



7.617 J 



FeO 



O.13 



O.I4 



0.13 





Si0 2 



O.17 



O.24 



0.21 





Na 2 



1.68 



1.68 



1.68 





MgO 



1.09 



1. 14 



1.09 







98.48 



99-59 



99.04 





- 20.796 



The analyses show that the mineral is essentially a hydrous 

 sulphate of iron and aluminum, the other oxides present being 

 simply impurities. In calculating a formula for the mineral, the 

 only difficulty that arises is with respect to the amount of water 

 which really forms a part of the mineral's composition. It is 

 highly probable, from the fact that the material has been gradually 

 drying out, that the water expelled at 1 io° C. was partly that of 

 crystallization and partly occluded. 



The ratio obtained from the mean analysis corresponds very 

 nearly to the formula Fe 2 (S0 4 ) 3 A1 2 (S0 4 ) 3 27H 2 0. Assuming all 

 the H 2 present as water of crystallization, then our substance 

 might be viewed as a mixture of the two minerals, coquimbite, 

 Fe 2 (S0 4 ) 3 + 9H 2 0, and alunogen, A1 2 (S0 4 ) 3 + 1 8H 2 0. 



Such a mixture would require the following percentages of the 

 oxides: — 



Mean analysis 

 reduced to 100%. 

 Fe 2 3 13.03 13.54 



A1 2 3 8.30 7.76 



S0 3 39.10 39.67 



H 2 39-57 39-03 



100 100 



