Mineralogy and Geology. : 5 * 
Neither does Kussin’s analysis correspond to the ratio 14: 12: 15, ~ 
_. whence Rammelsberg derives incorrectly (but correctly from 1:9: 12)» 
_ the formula K Si+341 Si, but more nearly to 14: 12: 164, though prob- 
mica from Unionville, Pa., occurring iw aealy granular masses, af- 
ry J. D. Darrack, in the Laboratory of J. C. Booth, (Min., 1850, p. 
? 
Si 46-75, £1 39-20, Fe trace, Mg 1:02, K 656, Ca 0:39, Ff 4-90 = 98°82, 
This gives for the ratio 1-61 : 18°32 : 24:29 = 1:05: 12: 15:91 or 
ei itd 12: 16. 
he Albbarfiives mica (Svaaberg) and ae ue hautl) nets 
petra 3°27 : 15°06 : 20-61 — 2°60 : 12 : 16-42 — 22: : 
Fuchsite, 2-33 : 17-88 : 2491 = 1°53: 12: 16 ie = dg: 12 16. ‘sn 
The first t corresponds to the ratio2: 9: 12, and formula R2 Si+-34 Si. 
Taking the Fuchsite at 14 : 12: 16, it gives the formula R Si+3A1 Si. 
Maza RODITE, Schaf héutl.—This pearly white biaxial mica and others 
- allied have afforded the following analytical pesHps 
VOM 1, Schafhautl ; 2, Delesse, (Ann. d. Mines, [4], xvi, 202, 
1849); 3, 4, Br rewer, of dus Vain Laboratory, (Min., 1850, 359) ; 5, 
Rammelsberg, (4th Supp., 75): 
Si Al #e Mn Mg Na K Ft 
3 Zillerthal 47°05 34°90 1:50 195 407 796 1:45—98°88, sy lng 
2. St. Etienne, 46:23 33°08 — Game 210 145 887 4:12, F trace=99°33, D. 
8. Monroe, Ct, 49-96 82 85 trace — 1 08 2 289 791 4-460, ot OTs 90-29, B 
4. = “60 = 1 undetermined 446 
5. Loe, doubtful, - . ve 36 3-06 06 — ‘ nd 155 10°25 «2°43, Gabe 29-90 06, R. 
«A mean of 4 determinations. 
The ratios are as follows, 
£; 317 : 16°35 : 2445 = 2°33 2 12:1795 =116:6: 897 
2, 2°65 : 16°46 : bide = Ne 742 > PSL e= 090: 6 + S46 
3,4, 2°63 : 15°35 : 25°96 = 2:05 : 12: 2029 = 1:02 : 6: 1014 
> 2°71 : 16:08 : ms 86 = mers 12:1861 =.1:01:6: 9380 
Rammelsberg and Delesse agree nearly in giving the ratio 1 : : 9 
Schafhiutl’s has the protoxyds a little in excess, and Brewer obtained 
an excess of silica. But it is probable that all come under the 
formula, R Si+2# Si, The mica of Monroe, Ct., occurs with aay spit 
and topaz in large scales, aggregated into wedge shapes. G—=2-79— 
281. The St. Etienne mica has G—=2-817; Rammelsberg’s 2°83] ; 
Schaf hautl’s 2872. In this species the oxygen te of ov" peroxyds 
xg ; : he Gilberti 
mson appears to be altered muscovite, or margarodite.* 
* The mineral Gilbertite has the aspect of a pearly white mica, occurring in scales 
often partly aggregated. The following are the analyses given; 1, Lehunt, of true 
hg from Co: cakes om. Min., i, 235); 2, Thomson, rnwall, different local- 
ity, 
Si i Mg Ga Fe Na P 
‘lL 45°15 4011 190 417 243 — =98-01, Lehun 
Rey 4780 32°62 160 —— 518 9:23 £00=100" 48, Catal 
el ves for th en of the protoxyds, peroxyds and silica, 2-48 : 
1876 2545, a te tie 159) 12 : 15°01. Dufrenoy deduces 2: 12: 16. Like 
