296 
DESCRIPTIVE MINERALOGY. 
As this mineral closely resembles what has been termed hypersthene, I submitted it to a 
chemical examination, chiefly for the purpose of determining the proportion of lime which it 
contains ; this, so far as composition is concerned, being the chief difference between pyro¬ 
xene and hypersthene. The composition of the Lake George mineral is as follows : 
Silica, alumina and oxide of iron,.56.94 
Lime,. 24.06 
Magnesia,.... 29.00 
The large proportion of lime places this mineral under pyroxene. The proportions of the other 
constituents also agree with those found in some varieties of this species. 
Westchester County. Pyroxene, in various forms, is often met with in the dolomitic 
beds of this county. The crystallized white variety, usually in six-sided tables, is found in 
the quarries at Sing-Sing and elsewhere. The common variety has .been found at Sparta. 
The dolomite, moreover, often contains a substance with the cleavage of pyroxene, but which 
is soft, and has a considerable admixture of carbonate of lime and magnesia. The external 
characters strongly resemble those of white lamellar pyroxene ; but the effervescence which 
is exhibited when the mineral is acted on by a dilute acid, shows that it is largely mixed with 
one or both the carbonates above mentioned. 
Dr. MacCulloch long ago remarked that in Tirey (Scotland), crystals of tremolite and 
sahlite are so confounded, that a single crystal sometimes contains both substances, as if 
there was a transition between the two minerals.* I have observed the same thing in the 
dolomitic limestones of Westchester and Putnam counties ; tremolite and pyroxene occurring 
in immediate contact with, and indeed running into, each other. Veins of glassy tremolite 
every where run through a dull white mineral, which has the cleavage of pyroxene. 
Pyroxene is also found near New-Rochelle ; but it is so closely associated with hornblende 
and serpentine, that it is not easy to identify it. 
Fig. 223 . i w ill only add, that Fig. 222 represents a crystal 
obtained by Dr. Emmons from Warren county. M or 
M' on o 145° 9b Fig. 223 is the form of crystallized 
pyroxene from Bytown in Canada. The latter figure 
is introduced on the authority of Prof. Shepard. M or 
M' on a? 134° 17'; a? on a? 131° 8 ; ; ron f 106° 6'; 
u on u 131° 8'; x on r 126° 36b 
In Massachusetts, crystals of diopside are found in 
limestone at Bolton, where the massive sahlite also oc¬ 
curs. In Connecticut, also, there are several localities 
of this mineral, as at Canaan and New-Milford. 
The variety Jeffersonite is found at the Franklin furnace, and elsewhere, in New-Jersey. 
Fig. 222. 
Brewster's Edinburgh Journal of Science. I. 225. 
