236 



PHYSIOGRAPHY. 



Green Malachite. 



Compound Varieties. Twin-crystals: axis of revolu- 

 tion perpendicular, face of composition parallel with the 

 longer diagonal of the prism; angle of revolution =180. 



Fig. 216. 



M 



This composition occurs in almost every variety, and 

 even in those masses which consist of columnar particles of 

 composition. It then seems as if both the faces of a prism 

 were present, forming a dihedral termination of each indi- 

 vidual of 123 37, while in fact there exists only one of 

 them. Fascicular aggregations of delicate crystals. Tu- 

 berose, globular, reniform, botryoidal and stalactitic shapes: 

 surface drusy, rough, sometimes smooth ; composition co- 

 lumnar, generally very thin, often impalpable. Very thin 

 columnar composition, produces a satiny lustre ; impalpa- 

 ble composition, is the cause of conchoidal fracture. Mas- 

 sive : composition as above. The composition often re- 

 peated ; granularly compound masses consist of columnar 

 ones radiating from a centre ; curved lamellar ones are 

 likewise composed of thin columnar indiviuals. The sur- 

 face of the second composition is often rough, and particu- 

 larly in curved lamellar compositions, covered with a white 

 coating. 



1., Before the blow-pipe, it decrepitates, becomes black, and is partly 

 infusible, partly converted into a black scoria. It is easily soluble in bo- 



