220 J. P. Cooke, Jr., on Cryophyllite. 
sum of the bases each separately determined as the mean of 
two analyses equals 45°03 per cent, while the sum of the bases 
Analysis of Cryophyllite from Rockport. 
: 2 4, 3 Mean. Oxygen. 
Silica, 61°53 51:54 51:65 51°37 51°36 5149 2746 
— of silicon, 329 $34 362 342 1:06==2852 
i 82 
Alumina, re 16-77 } i7 5 
Sesquioxyd of manganese, 033 0°35 034 O1 
Sesquioxyd of iron, 200 1°94 1:97 059= 851 
Protoxyd of iron, 8-00 7-96 798 176 
' 0-76 45°06 45°29 45:02 0-76 030 
Potasea, 1314 13-16 1315 2 
Lithia, 4:05 4-06 406 216== 6°45 
Soda, trace. trace 
Rubidia, “ 14°96 
99°94 
Oxygen ratio, 14:96 : 28°52 
14°26 
: : 28°52—1 : 2. z 
General formula, RO, SiO. Probable rational formula, (42? . #8), 385i): 
The fluorine in the mineral is so firmly incorporated that, as 
stated above, it is not driven out even by a red heat, and there 
ean be no doubt that it replaces a portion of the oxygen of the 
silica in the proportion of one equivalent of fluorine to every 
twenty-eight of oxygen. The ratio of the oxygen of the prot- 
