1 48 The Monoclinic Pyroxenes of Neio York State. 



of Crag Harbor near Port Henry, and is said to occur in regular 

 grains and imperfect crj^stals, (Ref. 21). 



Keene, Essex Go. — ^Black p3^roxene in ealcite is found at the 

 Weston Mine two miles southwest of Keene. The mineral occurs 

 intermixed with the ore, and also in streaks along the edges of 

 the ore bed. When surrounded by ealcite the pyroxene often 

 develops well bounded crystals, the ordinary form being a (100), 

 b (010), m (110), and c (001). One small crystal had the combina. 

 lion a (100), h (010), m (110), s(llO), and o (^21). (PI. XYI., Fig 

 2), Most of the crystals are decomposed and in section some- 

 times show an abundant deposition of magnetite grains along the 

 cleavage lines. In section the augite is slightlj^ pleochroic, the 

 colors being green to yellow. It also exhibits an intimate asso- 

 oiation with garnet, which may perhaps be an alternation product 

 of it. (Ref. 26). 



An analysis of the fresher portion of the material gave 



Percentage. Katio. Prop, parts. 



SiOa 56.00 .933 32 



FeO 2.40 .034 1 



CaO 21.63 .386 13 



MgO 5 23 .1307 5 



FeA 4.70 .029 1 



AlA 8.44 .082 3 



Alkalies 50 



Ignition 20 



99.10 

 Sp. Gr. 3.5 



From the above we obtain the formula Ca^^gMg^FciFegAlg 

 SigjOgg, which is resolvable into 



5 (CaMgSl^Og) 



CaFeSljOe 

 3(CaAl.,S108) 

 CaFeaSiOg 

 leaving SijjOae) which, is approximately Si02. 



Keene, Essex Co. — Dark green prismatic grains of augite are 

 abundant in the limestone near Keene. Their composition is 



Percentage. Ratio. Prop. Parts. 



SlOa 56.14 .935 467 



FeO 2.85 .039 19 



FeaOs 38 .002 1 



AlA 8.19 .080 40 



CaO 17.79. . .31 150 



MgO 13^ .34 170 



99.02 



