42 Reéxamination of American Minerals. 
and Horton of Monroe, N. Y., Professor Hume of Charleston, 
Mr. Markoe of Washington, and Mr. Samuel W. Johnson of the 
Yale Laboratory. 
In the analytical processes, with the exception of the alkali 
determinations, we have deviated but little from the methods 
on and alumina are i sg by ammonia with the previous 
addition of sal-ammoniac, but the precipitate is redissolved and 
reprecipitated three are before the separation is considered sat- 
isfactory ; in addition to this, the oxyd of iron and alumina are 
finally tested to ensure the absence of magnes 
A reéxamination of some of the minerals it noticed may 
cee of ce ane here given is to remove as far as act 
any existing doubts connected with; them. Moreover, in contin- 
uation of these researches, we propose to enter upon the reéx- 
amination of a number of well established species, in order, by 
additional a of them, to extend our knowledge of Ameri- 
can miner 
11. Chesterlite, identical with Orthoclase. 
This mineral occurs in implanted crystals on dolomite near 
East Bradford, Chester County, Pa. In physical characters it 
resembles orthoclase, but it has been considered triclinic, and 
Erni’s analysis* gave soda as the alkali. The crystals occur fre- 
quently as twins, and are often very much aii ea spe- 
cimens we have examined the angle T on I” varies from 121° 
to 127°—rendering it extremely difficult to duende the normal 
value of the angle; some of the measurements would however 
lead to the conclusion that it is monoclinic, since the angle of 
cleavage is by our measurements near 90°. So far as our opinion 
is concerned—based on both its chemical and physical charactet 
—we unhesitatingly aging it an orthoclase. 
wo analyses gay 
1 2. 
Silica, . ; 64:76 : : ; 65°17 
Jumi ; 17-60 : : ‘ 17°70 
Poroxyd of iron, : 59 ‘50 
Lime, : 65 : “56 
Magn : : 30 ‘: a" j 25 
Pith ‘ ; 1418 ; ; 13-86 
a, 175 164 
Ignition, . : 65 ; ? : 65 
100°39 100°33 
These correspond to the composition of orthoclase, and chemi- 
euly the mineral is identical with it ; if it shall be proved that the 
* Dana’s Mineralogy, si edit., p. 678. 
