88 J. D. Dana’s Mineralogical Contributions. 
ut when we meet with such a case as that of the feldspars, 
where the only constant ratio is that of the oxygen of the pro- 
toxyds and peroxyds, the oxygen of the silica varying, the 
law for the replacement of protoxyds by peroxyds seems to have 
no application. 
9. Anhydrite. 
Hausmann, in his paper on the system of crystallization of 
Anhydrite, (Karstenite), and its homeomorphism with the Bary- 
tes series,* arrives at the following comparisons :— 
= a:bse @ l-@ 1- 
Thenardite Na§ 0°7494:1:05918 118° 46’ 106° 18’ 76° 34’ (103° 26/) 
Heavy Spar Ba§ 07659: 1: 06234 116922’ 105° 6’ 78°18’ (101° 42’) 
Anhydrite CaS 0°7636:1: 06581 118° 42’ 105°16’ 81° 6’ ( 98° 64’) 
A closer approximation of Anhydrite is obtained by making the 
prism m, the vertical prism oc -3, and s the brachydome 4-@- 
Then the axes and the above angles become, 
Anhydrite, 073486 : 1: 059898 118° 35’ 107° 99" 77° 47 (102° 56’). 
Giving the crystal the position usually adopted for heavy spar, 
in which the above «, 1- &, and 1-% correspond respectively to 
-&,1- and o, the axes area: b: c=1°368: 1: 0:8083, while 
those of Heavy Spar in the same position are 1:3127 : 1 : 0-81413. 
The prisms m and s in this view, are ¢-@% and 2-&, and the oc- 
tahedral planes are m-n, 2m -2n, 3m-3n, With m=2 and ast. 
The cleavage in this case is brachydiagonal and basal, with 
the macrodiagonal less perfect. The divergence in crystallization 
of the sulphate of lime from the others of the series, is a parallel 
fact with that of the bisilicate of lime (Ga* Si?, Wollastonite ) from 
pyroxene. 
10. Valentinite or White Antimony and Senarmontite. 
Senarmontite is described as crystalling in the monometric sys- 
tem and Valentinite in the trimetric, the chemical species SbO* 
Oo 
tween the axis and intermediate diagonal of an octahedron, oF 
2: 1, and the vertical axis (a) equals nearly the sum of the two 
lateral (b-+c). 
* Poggendorff’s Annalen, bexxiii, 572, 
y 
