16 



PEOCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 71 



The matrix of these hirger gray-green twinned pyroxenes is in 

 all cases a pale gray-green rock of fine sugary texture which con- 

 sists of almost pure diopside. Examined under the microscope this 

 diopside is found to be essentially the same in optical properties and 

 hence probably in composition, as the foregoing crystals. 



An analysis of diopside from this locality made by Eakins doubt- 

 less represents the larger tAvinned crystals. This gave the following 

 results : 



Analysis of diopside crystals 

 [L. Q. Eakins, analyst] 



The specific gravity of the analyzed material is given as 3.312 

 at 16.7°. It is stated that the diopside is associated with vesuvianite, 

 scapolite, garnet, epidote, etc., which probably means the collection 

 as a whole rather than the individual specimen from which the 

 material for analysis came, since all of these minerals were in no 

 case found in a single specimen studied by the writer. 



If this analysis be recast into constituent molecules according to 

 the method of Washington and Merwdn the following table is 

 obtained : 



Diopside (CaMgSi.Oo) 83.75 



Hedenbergite (CaFeSi.Oo) 3.23 



Wollastouite (CaSiOa) 3.62 



Fe^Oa+AloOs 11. 67 



102. 27 

 Deficiency in SiO. 2.27 



Sum 100. GO 



Another and but slightly different type of diopside is found in 

 certain greenish-gray masses of massive pyroxene of very porous 

 texture, the cavities of Avhich are occupied by small crj^stals, some 

 of them, like the last, twinned on (100) and others simple, of an 

 acute pyramidal habit. The crystals reach a length of only 3 or 

 4 mm. Some of the twins show terminal faces of several forms and 

 others are very simply truncated by only c (001). One twinned 

 crystal from a specimen of this kind is illustrated in Figure 3. This 

 is the only doubly terminated crystal seen in this specimen, and the 



