Chemical formulas of the Silicates. 259 
Euclase, 3:2  (Ha,R,8R)sJOsJSi  (Fta+#Be+ZBAl)2]0.4Si 
Datolite, “ (Ha, R, dz)s]Os|Si (}2+$Ca+35p.)s] Oo] Si 
Prochlorite, “ (R, 8R)s|Os]Sitnaq ($R+38Al)s]Os|Si+1f¢aq* 
Cronstedtite, « “ (fR+46Fe)s| Os] Sit] faq 
Jorundophilite, 2:1 (R, BR),|Oo]Si+naq (4R+48R),] Oo] Si+2gaq* 
Chloritoid “ “ (ZR+48R), | Oc] Sitaq 
Margarite, “ (a, R, BR),| Oo] Si (44.+4R+§8R),]06[8i 
Thuringite, “ “ (dws+ZR+Z3R).[Oo]Si 
Seybertite,- 3:1 (R, BR)o] Os|Sitnaq (2R+3GR)e] Oc| SitJagt 
Xanthophyllite, 4: 1 (R, BR)=| O10] Sitnaq (@RF$GR)s] O10] Sitagt 
The species Ilvaite, from Elba, appears from the analyses to 
fall among Subsilicates. But the oxygen ratio between the 
basic metals and the silicon varies in the analyses from 5 : 4 to 
9:8; and in the mineral from Nassau, regarded as the same 
species (Tobler, Journ. Ch. Pharm., xcix, 122), the ratio is 1:1. 
Stideler states that 1 to 2 p. ¢. of water is always present which 
18 expelled only by the heat of ignition; and making the water 
basic, arrives at the ratio 5:4 for the species. Another view, 
quite as probable, considering the opacity of the species 
and Lechartier’s results with staurotide, is that the mineral of 
ba contains some ¥eli (Géthite) as impurity; and that 
causes the divergence from the ratio 1: 1. 
IV. InrermepraTe SILICATES. 
The silicates in which the oxygen ratio for the basic metals 
and silicon is between 1:1 and 1:2 have been called Parasth- 
cates by Odling, being regarded as combinations of a Unisilicate 
and Bisilicate. The ratio 
1:1}, occurs in Leucophane and Lepidolite, and would correspond to 1U + 2B 
11h “: Muscovite and Tolite, = : 140 +1B 
lily “  Nepheline, “ “ 34U +1B 
; See note i ie = 
Prom eee eno obtained but 160 pe of water, more than 
less than other analysts had found. 
+ From Meitzendorf’s analyses. 
