46 Geology and Mineralogy of a part of Massachusetts, &c 
20. Nacritre? 
On the mica-slate of Chester, is found a mineral, incrust- 
ing the rock, which may be nacrite. ‘I have not been able 
to examine it minutely, and merely mention it. Easily fu- 
sed. It may be a new variety of stilbite, occurring as an 
incrustation—its colour is a dirty yellowish white. 
21. TREMOLITE. 
Var. 1. Common. 
In flattened or bladed crystals in Great-Barrington, 
Sheffield, and New Marlborough in dolomite. At the 
last Md the dolomite resembles that at Kingsbridge, 
N. ¥., and also contains augite. Though the dolomite 
of Great Barrington containing the bladed crystals is 
generally very friable, I have found a large rock, which is 
very hard, and contains the same kind of crystals with au- 
gite. They are found sparingly also in Pittsfield. In Mid- 
dlefield in large masses of aggregated flattened crystals — 
with rhomb. spar. Emmons. These crystals often pass 
off into a perfectly granular tremolite. ‘This is a new an 
_ very distinct variety, and greatly resembles the white cocco- 
lite of Phillipstown, N. Y. opposite to Newburgh and a few 
miles from the river; but the product of fusion proves our 
mineral to be granular tremolite. ‘The constituents of coc- 
colite and tremolite are nearly the same, and the two min- 
erals seem to be nearly related. The locality, at which 
the bladed crystals are abundant, is in Muddy Brook in 
Great Barrington, three miles from the plain in Stock- 
bridge, and on the left of the road leading to New Marl- 
borough. In this friable dolomite I have found oblique 
four sided prisms of tremolite, which were friable, but har- 
dened somewhat, like the dolomite, on exposure to the alt. 
They are probably the primitive form of tremolite, 
Var. 2. Fibrous. 
In Lee, Sheffield, Salisbury, and Canaan, Con. 
e 
masses, whose fibres are sometimes more than two feet 
long, contain parallelopipeds of sulphuret of iron. 
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