ORDER IV. PRISMATIC AZURE-MALACHITE. 169 



Pr -f co, Pr + OD parallel to those with P oo 

 or also with P -f oo. The faces of some of the 



forms, as of _J_-TT__ 5 and of 1_L~ L. rough. 



Pr -f- oo sometimes concave, the greater part of 

 the other faces even and smooth. 



Lustre vitreous, almost adamantine. Colour vari- 

 ous shades of azure-blue, passing into blackish- 

 blue and berlin-blue. Streak blue, lighter than 

 the colour. Transparent ... translucent on, the 

 edges. 



Brittle. Hardness = 3-5... 4-0. Sp. Gr. = 3-831, 

 crystals from Chessy. 



Compound Varieties. Twin-crystals : face of 

 composition parallel, axis of revolution perpendi- 



Pr 

 cular to * Globular, reniform, botryoidal, 



stalactitic shapes, implanted and imbedded : surface 

 drusy and rough ; composition columnar, more or 

 less perfect and distinct, faces of composition 

 generally rough. Massive : composition columnar, 

 more rarely granular. Sometimes there is another 

 curved lamellar composition, the curved faces of 

 which often possess a darker colour than the rest, 

 and are covered with asperities. Rarely in an 

 earthy state. 



* A beautiful specimen of this rare variety is preserved in 

 the cabinet of Mr ALLAX. 



