266 F W. Clarke — Minerals of Litchfield, Mame. 



Ozarkite. 



H 3 0-_ 13-80 



SiO„ 36-85 



A1 2 3 29-42 



Feg0 3 1-55 



CaO .* 13-95 



Na 2 3-91 



K 2 



Rauite. 



Hydronephelite, 



11-71 



13-12 



39-21 



38 90 



31-79 



33-98 



•57 





5-07 



.05 



11-55 



13-21 







1-01 



99-48 99-90 100*27 



Inasmuch, however, as massive minerals, and especially those 

 which are produced by processes of alteration, are always sub- 

 ject to doubt, I requested Mr. Diller to assist me with a micro- 

 scopic examination of the new substance. He very kindly 

 acceded to my request, and I subjoin an abstract of his results. 



" A section was carefully prepared so as to show both the 

 sodalite and the white, lusterless mineral associated with it, in 

 such a way as to reveal their relations. The extremely irregu- 

 lar line of contact between the sodalite and its secondary pro- 

 ducts is well defined in transmitted light, but is even more dis- 

 tinct between crossed nicois from the fact that the sodalite, 

 being isotropic, remains dark in all positions, while the other 

 minerals are more or less brilliantly colored. The secondary 

 products, which have clearly resulted from the zeolitization of 

 the sodalite, are two in number. One of them forms very 

 much the larger portion, probably nearly 90 per cent of their 

 total amount, and the other is imbedded in the first in the form 

 of distinct grains. Under the microscope in transmitted light 

 the predominating mineral, which is doubtless a zeolite as 

 shown by your analyses, is more or less deeply clouded like 

 decomposed feldspar. Between crossed nicois it breaks up 

 into flaky grains which vary considerably in the intensity of 

 their color. Some remain dark, others range through light and 

 medium tints of red and yellow, according to the position of 

 the section. The isotropic grains in converging light are 

 proved to be distinctly uniaxial and positive, and the aniso- 

 tropic ones as far as can be determined exhibit parallel extinc- 

 tion. It is evident therefore that the zeolite must be either 

 quadratic or hexagonal in the system of its crystallization. 

 Some of the grains show an indistinct striation approximately 

 parallel to the vertical axis, but a distinct cleavage could not 

 be discerned. In basal sections three sets of fractures could 

 be rarely made out with sufficient distinctness to suggest that 

 the mineral is probably hexagonal. The mode of its occur- 

 rence indicates clearly that it has resulted from the zeolitization 

 of the sodalite; a phenomenon which has been observed in 

 many rocks. 





