Ill 



TAB. CCCLX. 



This variety of vitreous Copper Ore is also found at Cooks- 

 Kitchen, in Cornwall, but is very rare. I have received it 

 among other favours from Mr. J. Taylor of Tavistock. It 

 is worthy of remark, that the crystals are of a large size 

 to what is usual, and the hexangular pyramids, which are 

 placed base to base, are more or less elongated : thus has 

 Nature sported with the crystallization, so as to prevent our 

 measuring with certainty the angle of incidence at their 

 mutual bases. Some of the crystals have the regular bevel- 

 lings of Haiiy, perhaps, not to be measured with certainty; 

 and some of the crystals have many lateral faces, so as to 

 give roundness, thus also to elude measure. The fracture 

 is mostly irregularly glassy, or minutely conchoidal. This 

 Ore is easily scraped or scratched with a knife to powder, 

 but is not brittle. The colour is iron-grey within, darker 

 on the outside : some specimens have the blue watch- 

 spring lustre and iridescence. Spec. Grav. t according to 

 Kirwan, 4.129. 

 By analysis it is found to contain : 



Copper . . . 78*5 



Iron ' . . . 2*25 



Sulphur . . . 10*5 



Silica .... 0*75 

 The matrix is a mixed sulphuretted Oxide of Copper and 

 Iron* with Quartz, through which there runs a vein of the 

 vitreous Copper Ore with the crystals. 



* The black Copper Ore of Kirwan, 2.143. Kupfer Schwarlze of Werner. 

 This may, perhaps, serve as a sufficient specimen for this work. 



This dusty or earthy ore generally accompanies the sulphurets, or other 

 copper ores. It is yellowish, reddish, or brownish black. Scarcely soils. Is 

 rather heavy. Contains about half its weight of copper; but, from being ge- 

 nerally produced by the decomposition of the other ores of copper, it of course 

 Taries much. 



