7 ( 2 



The faces are sometimes smooth, mostly bright, and oc- 

 casionally show signs of the angles of the tetraedron, or 

 have stris parallel to their edges, as Count Bournon ob- 

 serves. He also remarks that the four planes terminate in 

 one and the same point ; but more commonly the apex is • 

 formed into a ridge, the octaedron being lengthened pa- 

 rallel to the lesser inclined planes. The base is then a 

 square, or at least approaches nearly to that form. The first 

 figure seems to be rare ; those with the ridge are more com- 

 mon, particularly such as are further lengthened, passing 

 from the right hand figure in my Plate to the left*. The 

 gangue is an ochraceous quartz with some copper, and often 

 approaches what is called pitch copper: the right hand 

 figure has a little green globule of a waxy appearance. Such 

 are sometimes abundantly scattered over the octaedral crystals, 

 and appear to be carbonate of copper, or malachite. 



It is either of a beautiful deepish azure Hue with a 

 greenish cast, exactly resembling pure Roman vitriol, or 

 artificial sulphate of copper somewhat opaque, or of a fine 

 green ; in which last case it resembles the emerald. Such 

 specimens are most transparent, and vary in being some- 

 times lighter coloured. These are frequently blue within, 



* The Count mentions these as the only two varieties he has observed in 

 the form of the crystals of this species, although he had opportunity of exa- 

 mining a great number of specimens. I am happy to add a new, and I think 

 interesting, variety, especially as it seems, from what has been said above, to 

 be very rare. See tab. 32. 



