114 



PROCEEDING OF THE ACADEMY OF 



[Vol. LXXIV 



Wavellite, Llallagua, Bolivia 



The Llallagua tin mines are situated on the northeast slope of 

 Cerro de Llallagua, about . 100 kilometers southeast of Oruro, 

 Bolivia. The deposits are phenomenal, and form the richest known 

 mines of cassiterite. The ore bodies are distinct fissure fillings, or 



Fig. 1-3: Wavellite; 1. Llallagua, Bolivia; 2. Trimble's Mine, Chester 

 County, Pennsylvania; 3. Hellertown, Lehigh County, Pennsylvania. 



mineralized brecciated zones, in a quartz-porphyry which forms the 

 core of the mountain. The principal metallic minerals are cassit- 

 erite, pyrite, wolframite, and bismuthinite. 



The wavellite occurs locally in vugs in the quartz-pyritic portions 

 of the veins. Frequently three generations of wavellite crystals 

 are to be seen. 



The crystals are colorless, the smaller individuals being quite 

 limpid. The luster is vitreous, excepting on the unit prism m 

 (110), which is pearly. The mineral also occurs at Llallagua in 

 pale greenish stalactitic masses. The largest specimen in the 

 Vaux Collections is a slab measuring 25 X 35 cm., and entirely 

 covered with wavellite crystals. The crystals show the usual 

 tendency to form subparallel aggregates, with distinct individuals 

 in the cavities. 



Preliminary measurements were made on twelve crystals, of 

 which half were rejected due to subparallel growth present in the 



