424 E. V. Shannon — Notes on Boulangerite. 



associated with, pyrite and drusy quartz along a rift in 

 a mass of white vein quartz containing disseminated 

 pyrite crystals and fibrous masses of boulangerite. They 

 reach a maximum length of about 1 millimeter, and are 

 highly polished with metallic luster and light lead-gray 

 color. They are all tabular parallel to the front pinacoid 

 a (100) and seem to possess a distinct cleavage parallel to 

 this plane. Several of the crystals were detached from 

 the matrix and measured with a Goldschmidt 2-circle 

 goniometer. 



The crystals are all similar in habit, the dominant forms 

 being the macropinacoid a (100), the prism 72(120) and the 

 pyramid ^(124) while several other prismatic forms occur 

 as narrow faces, the form and habit of the crystals being 

 illustrated in fig. 1. The prism zone is strongly striated 

 vertically. 



The angles measured were found not to be in entire 

 agreement with those given for the same forms by Sjogren 

 and a question arose as to the advisability of substituting 

 new axial values for this mineral. To this end the descrip- 

 tion of the mineral from the Swedish occurrence was 

 carefully considered. The crystals from Sala, which 

 seem to have been very minute, were obtained by dissolv- 

 ing the carbonate gangue with dilute hydrochloric acid. 

 Although Sjogren states that the forms in the prism 

 zone gave quite good angles, the crystals are said to have 

 been strongly striated vertically and it seems probable 

 that the quality of this zone on the present writer's crys- 

 tals was fully as good as that on the crystal examined by 

 Sjogren. He states clearly that the measurements 

 recorded in his table were made on one and the same 

 crystal on which the only terminal face was found, the 

 dome ^^ (012), upon which he bases his value for the c axis. 

 This yielded only one measurement which was so poor 

 as to be scarce usable at all. Five crystals from the Idaho 

 occurrence were measured and on each of these the prism 

 ^(120) and the pyramid ^(124) were present as distinct 

 faces yielding good signals although the angles measured 

 varied somewhat. By weighting each angular measure- 

 ment according to quality the following average is 

 obtained for the form n{120) : 



n (120) ^ = 44°23' /> = 90°00' 



while the pyramid <e(124) gives the following average 

 angles : 



■ z (124) c^ = 44°47' P^25°48' 



