Chemistry and Physics. 421 
folie. Exfoliation commences at 500° to 600° Fahr., and takes 
place with so much force as often to break the test-tube in which 
the mineral is 1-2, the specific gravity 2°756, the luster talcose, and 
the color grayish, somewhat brownish. It was analyzed - 
ey, who “separated with great care from the base the scaly min- 
eral, which is the true vermiculite,’ and his results were as 
follows :— 
Oxygen Ratio. 
ie i True. App. 
Silica... __. 35°74 19°06 19°06 11 35°74 19°06 19°06 2 
mining .... 16°42 “765° 6b 4 1642 76 
Oxygen Ratio. 
i. App. 
2°23 
--.. 27°44 10°98 18°21 7 27°44 10°98 1098 1 
_ eRe 10°30 916 916 5 1030 916 916 1 
2 101°03 
The results of analysis in column 1, and the portions of the 
description of the mineral in quotation-marks, above, have been 
taken from “ Dana’s System of Mineralogy,” fifth edition, page 
493; and the atomic ratio which is there deduced is, 
Iv VI It It 
Si:R: A: Hell: 4: 7: 5. 
of the iron belongs with the sesquioxide radicals, the analysis 
would appear as in column 2, and the atomic ratio is then seen to 
eg: T: 7 : 1, which is undoubtedly the correct result. 
In the year 1851, Mr. W. W. Jefferis, of West Chester, Pa., 
new species (this Jour., LU, xli, 248, 1866), and named Jefferisite. 
Several years later, Mr. John Hall, now of Philadelphia, sent to 
me tor examination some rough six-sided prisms of a micaceous 
mineral, which he had discovered at East Néingham, in Chester 
County, Pa. This mineral also exfoliates when heated. It is a 
new species, and I have named it, after the discoverer, Hallite. 
4 year since I received from Colonel C. W. Jenks, in connection 
With other minerals from his corundum mine on the Culsagee river, 
