The Monoclinic Pyroxenes of Neio York State. 151 



combination of forms is m(llO), &(010), c(OOl), ii(Tll), o(221), 

 andsdll). 



A second variety in the same collection is a cluster of very 

 small glassy crystals of a grayish white color. They are ^-\ in. 

 long, with the ends rounded, but the faces in the prismatic zone 

 are a (100), m(llO), &(010). An analj-sis of the common green 

 variety gave : 



Percentage. Ratio. Prop, parts. 



SiOa 54.57 .9061 50 



FeO 1.301 .018 1 



CaO 21.42 .3825 21 



MgO 18.56 .464 26 



AlA 3.09 .0302 2 



Alkalies 40 



Ignition 15 



99.39 



From the above we obtain the formula 



Ca2iMg2eFeiAliSi3oOi3„ or (Ca,iFeiAl,)Mg26Si5oOi54. 



This is close to diopside in composition but, on account of the 

 high percentage of alumina is placed under augite. 

 Sp. Gr. 3.20. 



C:C 41° 30^ 



Na. 



a 1.6806 



,3 1.6843 



7 1.7036 



7 — a .0230 



2H 78° 57' 



2V 59° 40' 



Port Henry^ Essex County. — Pyroxene of a jet black color 

 occurs in close association with the magnetite at this locality. 

 Massive and granular specimens are not uncommon, but crystals 

 are rare. There is a fine group of crystals in the collection of 

 Prof. Kemp, which were found in the Cheever mine at Mineville, 

 four miles northwest of Port Henry. The pyroxene is associated 

 with granular magnetite and labradorite, and occurs on the edge 

 of the orebod}'^. Wheji it is intergrown with the magnetite it 

 shows no crystal faces, but when surrounded by the feldspar well 

 developed ones occur. The crystals (PL XIV, Fig. 8) are about 

 half an inch long and nearl}^ the same thickness. In the pris- 



