316 Spencer — Diaphorite from Montana and Mexl 



ico. 



Art. XXX. — Diaphorite from Montana and Mexico ; by 

 L. J. Spencer. 



Diaphorite being a rare mineral known from only a few 

 localities, it seems worth while to record two new occurrence-. 



A stephanite specimen from the LakeChelan district, Okano- 

 gan County, Washington, recently acquired by the British 

 Museum, shows crystals of dolomite, quartz, galena, pyrargyrite 

 and diaphorite. On a measured crystal of diaphorite the fol- 

 lowing forms were noted : a, b, m, tt, x, i/r, y, <o and (212). 



The Mexican crystals of diaphorite from Santa Maria de 

 Catorze, in the state of San Luis Potosi, are associated with 

 crystals of miargyrite, dolomite, quartz, pyrites and blende ; 

 they are very rich in faces and several new forms have been 

 noted. 



Except for the lamellar twinning sometimes present on 

 freislebenite, the three minerals andorite, diaphorite and 

 freislebenite are very similar in appearance, and can only be 

 distinguished by measuring the crystals. Between them an 

 interesting morphotropic relation exists, which reminds one of 

 the relation between humite, chondrodite and clinohumite. 



Sp. gr. Chem. comp. 



Andorite %b : a : c = 9846 : 1 : 0*6584 5-35 RS . Sb 2 S 3 



Diaphorite 2a : b : c = 0-9839 : 1 : 0-7345 5-9 



Freieslebenite.. f a : b : c = 0-9786 : 1 : 0-9277: 63 5RS . 2§b.,S 3 



(3 = 87° 46'' 



The vertical axes are in the ratio 9 : 10 : 13. The same rela- 

 tion can also be extended, though less perfectly, to stibnite on 

 the one side, and to bournonite, etc., and galena on the other. 

 This suggests that in composition also diaphorite should fall be- 

 tween andorite and freislebenite. Brongniardite,* which has an 

 intermediate formula, namely 2RS . Sb 2 S 3 , agrees in specific 

 gravity and in its external characters with diaphorite : it there- 

 fore seems highly probable that brongniardite and diaphorite 

 are identical. It is hoped to be able to collect sufficient mate- 

 rial (measured crystals of diaphorite) for analysis, in order to 

 definitely prove the identity here suggested. 



British Museum of Natural History. 



* The so-called cubic crystals of brongniardite have recently been shown to be 

 stanniferous argyrodite (Min. Mag., 1898, xii, p. 5). 



