The MonocUnic Pyroxenes of New York State. 169 



SiOa ......54.86 



FeO 1.30 



CaO 24.13 



MgO 18.14 



ALA 75 



Alkalies 35 



Ign 10 



99.89 

 Sp. Gr. 3.29. 



This corresponds very closely with an analysis made by E. L. 

 Sperry and given in Dana's System of Mineralogy, which is: 



Percentage. Ratio. Prop, parts. 



SiOi 55.12 .9186 235 



AI2O3 40 .0039 1 



FeO 1.12 .0155 4 



CaO 25.14 .449 115 



MgO 18.15 .4537 116 



K2O 02 



Na,0 45 



Ign 17 



100.47 



=:Caii5 Mg,i6 Fe4 AI2 Sijso O708. 



Sp, Gr. 3.286. 



The above analysis gives us the formula Ca^ ^gMg^ ^gFe^ 

 Al2Si235O708 which corresponds \&vy closely to the diopside 

 formula, CaMgSigOe. 



The optical constants of this diopside were determined as fol- 

 lows : 



C : C = 40° 



Na. 



a 1.6749 



/? 1.6852 



7 1.7013 



y—a .0264 



2 W 77° 42^ 



2 V 59° 30^ 



2E 114° 40' 



It will be seen that the indices of refraction are somewhat 

 higher than those given below. 



K. Zimanyi (Ref. 60) obtained the following values for diopside 

 from DeKalb. The determinations were made on plates cut per- 

 pendicular to the first and second middle lines, and were 5.8 and 



