^8 Mr. William Phillips's Descrlpflon 



are replaced by three triangular planes as shown in fig. 7. J have 

 also others which have the edges replaced, and in which each of the 

 angles is also replaced by both modifications (fig. 8.) The crystals 

 above described vary in colour from light and almost transparent 

 green, to dark green, sometimes having a brownish tinge: others are of 

 a resinous appearance and are almost transparent. It may be remarked 

 that the crystals of this substance are generally more or less, though 

 not regularly striated on the surface, and that the strise constantly 

 take the directions described in fig. 2 : they do not however admit 

 of a fracture in that direction, nor have I satisfactorily obtained it in 

 X\i^ direction of the faces of the cube. Some crystals of a dull green 

 colkbur, on being broken, have been found to enclose other cubes of 

 a darker colour, and iridescent on the surface. I have to regret 

 the impossibility of giving the admeasurements of the various angles 

 formed by the modifications and varieties of the crystal of the arseniate 

 of iron, on account of their minuteness. > 



Description of the red Oxyd of Copper. 



This substance, which during the last ten years, has been found in 

 Cornwall in great abundance, was previously of very sparing occur- 

 rence in that county. I am not aware of its having been mentioned 

 as a production of that district, by any foreign mineralogist, until 

 very lately : even the celebrated Haiiy has not quoted it in his 

 Traite de Mineralogie as a Cornish mineral. Many cabinets how- 

 ever now abound with it. Previously to the labours of Mr. Chenevix 

 on this substance its composition was by no means well understood. 

 From the analysis by that able chemist it appears to contain cop- 

 per 88,5, oxygen 11,5, and is therefore a sub-oxide of copper, and 

 " exists in a state hitherto unknown in nature." In reference, doubt- 



