KEELEYITE, A NEW LEAD SULFANTIMONITE FROM ORURO, BOLIVIA. 



By Samuel G. Gordon. 



The Oruro district of Bolivia has long been known to miner- 

 alogists by the excellent crystals of andorite, stannite, and other 

 rare minerals which the mines have produced. The present paper 

 is descriptive of a new lead sulfantimonite, keeleyite, which was 

 obtained on the Vaux-Academy Andean Expedition of 1921. 



The silver-tin mines of Oruro are situated in the hills at the 

 western edge of the town, and are three in number: the Socavon, 

 the San Jose, and the Itos. The keeleyite was obtained at the 

 San Jose mine. 



The ore-veins are essentially pyritic bodies forming fissure fillings 

 in a quartz-porphyry, and the dark Paleozoic slates into which 

 the porphry has been intruded. The principal minerals are pyrite, 

 light-brown massive cassiterite, tetrahedrite, and jamesonite(?). 

 Andorite and stannite are extremely rare. 



The exact mode of occurrence of the keeleyite is not known, 

 as the single specimen brought back was obtained at the cancha 

 of the mine. This specimen, measuring 3 X 5 X 7 inches, is a mass 

 of cavernous quartz, studded with small white quartz crystals. 

 The cavities contain sheaf-like aggregates of acicular crystals 

 of keeleyite, some pyrite, and an undetermined sulfide. 



General Description. Keeleyite is dark gray in color, and gives 

 a grayish-black streak. The luster of the mineral is bright metallic. 

 The hardness is about 2. The specific gravity was determined 

 in H 2 Oin a 5 cc. pycnometer and gave the value 5.21 ±. 



The mineral occurs in aggregates, usually radiating, of acicular 

 crystals which may measure an inch in length. The crystals are 

 deeply striated and furrowed, due in part, perhaps, to parallel 

 growth. No measurable crystals were found, but the mineral 

 is probably orthorhombic. 



Keeleyite fuses at 1, and gives the same reactions before the 

 blowpipe, etc., as the other lead sulfantimonites. A white sublimate 

 of antimony oxide is obtained by heating in the closed tube, while 

 dense white fumes are obtained in the open tube. The mineral 

 is almost entirely volatilized on charcoal, with the formation of a 



(101) 



