L. V. Pirsson — Crystallization of Enargite. 215 



most interesting crystals which have been observed among 

 these specimens however are represented in fig. 6. They are 



Fig. 5. Fi 8'- 6 - 



rather thick tabular in habit and attached by one end of the 

 macro -axis like those just described. They consist of the 

 planes c, (001) ; a, i'-l (100) ; m, 7(110) ; j, i-S (130) ; s, 1-2 

 (011) and a, |-3 (134). The planes of 130 are dull and do not 

 reflect light well, while the other prisms are extremely brilliant, 

 giving a good reflection of the signal, as do also the dome 

 1-z (011) and the brachy-pyramids f-3 (134). It was noticed 

 on these crystals, of which several good examples were exam- 

 ined, that the dome and brachy-pyramid always appeared only 

 at one end of the prism, the other being simply cut off by 

 the base (001). Moreover the upper base (001) is apt to be 

 dull and not to reflect light well, while the lower one (001) is 

 very brilliant and striated by oscillation with the unit macro- 

 dome (101). These facts would seem to point toward the 

 species being hemimorphic. Of the forms observed upon 

 these crystals the following are new to the species e, \-i (012) ; 

 v, i-2 (210) and s, f-3 (134). The following table gives the 

 calculated and measured angles by which the forms were iden- 

 tified. 



Planes. 



Calc. 





Meas. 





in,\m, 



110/sllO 



82° 



07|' 



82° 3', 



82 c 



17', 



82° 04 



a ^h, 



100-^120 



60 



H 



60 3, 



60 



20, 



59 45 



a y^V, 



100^210 



23 



12 



23 13, 



23 



18 





m ^ v, 



110^210 



17 



31 



17 28, 



17 



42, 



17 19 



my\l, 



110/sl30 



28 







28 24 









c s^Jc, 



001^101 



43 



261 



43 01 









c ^s, 



001/sOU 



39 



31 



39 39, 



39 



10 





s ^z, 



011^134 



13 



45£ 



13 45, 



13 



49 





Z A 2, 



134^134 



22 



45f 



22 46 









C /\Z, 



001^134 



33 



31 



33 33, 



33 



40 





The form f-3 (134)_was also identified by being in the zones 

 o (001) ^l (130) and m (110) A s (011) which have probably in- 

 fluenced its appearance. 



The powder of these crystals tested in the open tube gives 

 abundant reaction for arsenic and none for antimony, from 

 which we may conclude that they are very pure enargite, not 

 more than a trace at most of famatinite, the isomorphous anti- 

 mony compound Cu 3 SbS 4 , being present. 



Mineralogieal-Petrographical Laboratory. 

 Sheffield Scientific School, New Haven, November, 1893. 



