Miner alogical Notices. 411 



transmitted in that manner would alter in character with the 

 distance of transmission to an extent inconsistent with observed 

 facts. 



I am gi-atified to find, that the account which I have given of 

 Laplace's theory of sound is approved of by Professor Stokes and 

 by Mr. Haughton. 



London, April 2, 1851. 



LV. Mineralogical Notices. 



ENARGXTE, BY MM. BREITHAUPT AND PLATTNER. 

 [PoggendorfF's Annalen, vol. Ixxx. p. 383.] 



THIS mineral constitutes a veiy abundant ore of copper, which 

 is worked at Morococha, district of Jouli, in the Cordilleras of 

 Peru. It occurs there in general in compact masses, containing 

 sometimes crystalline druses, and forming a vein in a crystalline 

 limestone accompanied by Tenuantite and copper and iron pyrites. 

 This mineral has rather a lively metallic lustre analogous to that 

 of oxide of manganese (acerdese or manganite) ; its colour is black, 

 and likewise its powder. Its crystalline form appears to belong 

 to the right rhombic prism ; the crystals have generally the 

 primary prism based and truncated upon the vertical edges 

 parallel to the diagonal planes. The angle of the prism could 

 be accurately measured; it is 98° 11'. M. Breithaupt observes, 

 that such a prism might be derived in a veiy simple manner 

 from a prism of 120°; it would then have the formula Za:2b; 

 this, however, is merely accidental, as the crystals do not exhibit 

 the conditions of symmetry which would pertain to a regular 

 hexagonal prism. 



Enargite exhibits two perfect cleavages parallel to the faces of 

 the primary prism ; there are likewise distinct cleavages in the 

 direction of the diagonal planes, and an indistinct cleavage in 

 the direction of the base. The fracture is uneven ; it is brittle 

 and easily pulverized ; hardness exactly equal to that of calcareous 

 spar; specific gravity i-430 to 4-445. It is readily distinguished, 

 according to M. Breithaupt, by the perfect nature of its two pris- 

 matic cleavages, and by their angle which may be measured with 

 the greatest precision with the refiective goniometer. 



Heated in a closed tube, this mineral decrepitates violently, 

 furnishes a sublimate of sulphur, tlien fuses into a globule below 

 a red heat and loses more su]i)hur, acconi])anie'd by sulphuret of 

 arsenic. Heated in an open tid)(!, it gives oiF sulphurous acid 

 and oxide of antimony. On charcoal it disengages sulpluirct of 

 arsenic, and forms a deposit of arsenious acid, oxide of antimony, 

 and oxide of zinc. After being roasted, it gives with borax the 



