The Monoclinic Pyroxenes of Neiv York State. 149 



Lyon Mountain, Clinton Go. — The Bostonite dikes near Lj'on 

 Mountain contain augite associated with plagioclase and olivine. 

 The augite occurs in irregular grains or idiomorphic crj^stals, 

 showing a (100), 6 (010), and m (110). It is usually of a rose tint 

 and shows slight pleochroism. The large, well-formed crystals 

 show a decomposed granular core, and alteration to chlorite is not 

 uncommon. The extinction is about 45° (Ref. 15). 



Mt. Marcy^ Essex Go. — Diallage is said to occur in broadh^ 

 foliated dark green masses in the gabbros of Mt. Marcy (Ref. 30). 

 The composition of it is 



Per cent. Ratio. Prop, parts. 



SiO^ 46.28 .7811 56 



TiOa 59 



FeO 14.80 .2055 15 



CaO 18.78 .3353 24 



MgO 8.91 .2227 16 



FeA"' 2.21 .0138 1 



AI2O3 7.38 .0720 5 



H2O 1.115 



100.065 

 Sp. Gr. 3.386 



This calculated, gives the formula. 



Ca24Mgi6Fei5Fe,AlioSi560i75 



This can not be resolved into a mixture of isomorphous sili 

 cates, and it seems therefore more reasonable to consider the 

 ferric iron and alumina to be present as oxides, and we therefore 



get 



Ca^iMgieFeisSiseOieT+FePs+SAl^Og. 



The pyroxene formula can then be resolved into the following 



metasilicates : 



15 (CaFeSijOg) 

 9 (CaMgSi^Og) 

 7(MgSi03) 



Natural Bridge, Lewis Gounty. — The pyroxenes from this 

 locality are generally embedded in calcite. As Natural Bridge 

 lies almost on the boundary line between Lewis and Diana Town- 

 ships, it is probable that many of the crj^stals labeled " Diana " 

 come from the former localit}'. 



A number of augite crystals were collected by the writer at 



Annals N. Y. Acad. Sci., IX, May, 1896.— 11 



