79 



TAB. CXLIL 



ARGILLA hydrata. 

 Hydrate of 'Argill, or Hydrargillite. 



Class 2. Earths. Order 1. Homogeneous. 



Gen. 1 . Argill. Spec. 2. Hydrate. 



According to our expectation before expressed, we are 

 enabled to give figures from Cornish specimens of this 

 substance by favour of the Rev. Mr. Gregor, who lent us 

 his best specimen, which is represented in the upper Jigure. 

 This is in looser radii than those from Barnstaple, but ap- 

 pears to agree precisely in the form of the crystal, which, 

 according to our idea, shows more of the primitive faces, 

 (viz.) the flat sides of the column, as that shows only one 

 primitive face at the apex. We could not attempt to 

 measure these crystals, they are so extremely small. The 

 gangue is also different. We retain Mr. Davy's name of 

 Hydrargillite, although Mr, Gregor believes there is an 

 acid contained in it, but it is not determined what acid, or 

 whether it is essential to the mineral. It is formed in the 

 hollows of the rock or gangue, with Quartz crystals coloured 

 with red Oxide of Iron more or less sticking in mammillae 

 about them, probably mixed with Oxide of Copper; but it 

 has not undergone regular examination. On some parts 

 of the gangue there appears to be Oxide of Uranite: see 

 tab. 124; and Mr. Gregor, by some trials made with small 

 quantities, thinks it contains, beside Uranium, a little 



