6RDERIV. PRISMATIC OLIVE-MALACHITi:. 165 



Streak olive-green ... brown. Semi-transparent 

 ... opake. 

 Brittle. Hardness = 3-0. Sp. Gr. = 4-2809. 



BODRNON. 



Compound Varieties. Globular and reniform 

 shapes : surface rough, sometimes drusy ; composi- 

 tion columnar, generally very perfect, straight and 

 divergent, rarely promiscuous. If the composition 

 be very thin, the lustre becomes pearly. Massive : 

 composition columnar. Sometimes repeated com- 

 position ; granular and columnar ; curved lamellar 

 and columnar. The faces of the first composition 

 rough, of the second composition smooth, 



OBSERVATIONS. 



1. The prismatic Olive-malachite has been found to con- 

 sist of 



Oxide of Copper 50-62 50-00. 



Arsenic Acid 45-00 29-00. 



Water 3-50 KLAPROTH. 21-00. CHENEVIX. 



Alone it remains unchanged before the blowpipe. Upon 

 charcoal it melts, with a kind of deflagration, and is reduced. 

 A white metallic globule is formed, which in the process of 

 cooling becomes covered with a red coating of sub-oxide of 

 copper. In some varieties a scoria is formed round the me- 

 tallic globule. This mineral is soluble in nitric acid. 



2. It is found in veins, chiefly consisting of various ores of 

 copper and rhonibohedral Quartz. It is . accompanied by 

 these, and by prismatic Iron-ore and decomposed Iron- 

 pyrites. 



3. It occurs in the copper mines near Redruth in Corn- 

 wall, and has been lately discovered in Tynehead mine, 

 near Alstonmoor iu Cumberland. 



