L. V. Pirsson — Crystallization of Enargite. 213 



have been kaolinized and often entirely removed ; the enargite, 

 frequently accompanied by free gold, being deposited as a sec- 

 ondary process in the cavities thus formed. The groundmass 

 of the porphyry retains to a considerable extent the form of 

 the feldspar phenocryst and the masses of enargite are thus 

 pseudomorphous in shape. 



While generally in compact masses or 

 with the crystals so crowded as to be indis- Fi 8- L 



tinct, at times the cavities are lined by 

 small glittering prisms of a bluish black col- 

 or, in size up to tlyee mm. in length. They 7n n \j{h 

 are very tabular from a large extension of 

 the macropinacoid i-l (100) and appear as in 

 fig. 1, being composed of the following sim- 

 ple forrasa, i-l (100) ; c, O (001) ; m, 7(110) 

 and h, i-2 (120). The forms were identified by the following 

 measurements. 



Calc. Meas. 



h ^m (110^110) = 82° 7' 81° 22' 81° 37' 



m A Ji (120a120) = 59 43 59 55 60 16 



In these, as in the following in this article, the calculated 

 angles are derived from the fundamental angles assumed by 

 Dauber in which (11 0) ^ (110.) = 82° 7£' and (001) /v (011) = 

 39° 31' the axial ratios derived from these being 



d: b:c : : 0-8712 : : 1 : 0-8248 



The prisms of these enargite crystals are strongly striated in 

 a vertical direction, which accounts for the deviation in the 

 calculated and measured angles. The base is not striated, but 

 is rough and does not reflect light well. 



Enargite from various American localities has been analyzed 

 and described by several authors. These may be briefly men- 

 tioned as follows : 



Brewer's Mine, Chesterfield, South Carolina, analyzed by 

 Genth.* Willis Gulch near Black Hawk, Colorado. Described 

 by Burton. f Morning Star Mine, Monitor District, Alpine 

 Oo., California. Analyzed by Root.J Tintic District, Utah, 

 described by Silliman,§ where it occurs at several mines, mate- 

 rial from the Shoebridge Mine having been analyzed by E. S. 

 Dana. [| 



No crystals are mentioned as being suitable for crystallo- 

 _graphic work, the various authors describing the material from 



*This Journal. II, vol. xxiii, j). 420, 1857. 

 t This Journal, II, vol. xlv, p. 34, 1868. 

 % This Journal, II, vol. xlvi, p. 201, 1868. 

 §This Journal, III, vol. vi, p. 126, 1873. 

 || Op. cit. 



