Chemistry and Physics. 431 
It is evident from these analyses that the atomic ratio of the min- 
eral is 2: 1:1: 1, and its formnla may therefore be written :— 
R,, RB. O,,.S, . 3H, 0 
vermiculite corresponds to its more usual type. We give below, 
at (1), the results of an analysis of Vesuvian Biotite, by Chodnef; 
and, at (2), the same, assuming that a portion of the iron is in the 
ferrous condition, as is well known to be the case, in order to show 
that values within the probable error of the analysis would give 
the ratio 2:1:1. Here, of course, the alkali takes the place of a 
portion of the magnesia of the vermiculite. 
Si Al Fe Fe Mg Oa K 
(1) 40°91 17°19 11°03 19°04 0°30 9°96—=98°43 
(2) 40°91 17:19 7:03 4:00 19°04 0°30 9:°96=98°43 
21°82 830 211 ‘89 7°62 0-09 1°69 
eos ad 
21°82 10°41 10°29 
2°12 101 I 
This new variety of vermiculite is so well marked, and the com- 
position so definite, that I have thought best to designate it by the 
tion of the iron: I have therefore made an assay of the iron by 
be ae method I formerly described in this ournal, xliv, 347, 
Xi 
Steatite with which it is mixed; and this steatite was pore the 
Poating of the greater part of the small quantity of te 
family of minerals, 
Hallite.—Several years since this variety of vermiculite was 
Sent to me by Mr. John Hall, of Philadelphia, by whom it was orig- 
Inally discovered. The examination then made showing th 
mineral was a new variety, if nota ies, of | 
ite, in recognition of the min- 
eralogical services of Mr. Hall, who not only discovered the min- 
