II. On the Oxyd of Uranium^ the production of Cornwall^ together 

 'With a description and series of its Crystalline forms. 



By William Phillips, Member of the Geological Society. 

 Read February 17th, 1815. 



Ti 



HE only mine In Cornwall which until within the last few 

 years was known to have yielded the oxyd of uranium, was that 

 called Carharack, which was situated about two miles nearly south 

 of St. Die. The crystals on a specimen from that mine in my 

 possession are tabular, of a green colour and transparent, except 

 such of them as are partially or wholly coated by a deposition of 

 an ochreous substance, similar to that termed gossan by the miner. 

 This substance also is interposed between an aggregated quartz 

 tinged with iron, and the crystals j some of which are imbedded iii 

 it. It may therefore be termed, in regard to this specimen, the 

 matrix of the crystals. On many of them have been deposited 

 numerous minute cubes of a light green colour ; which, as there is 

 a considerable deposition of cubic arseniated Iron in a cavity of 

 the same specimen, I consider to be that substance rather than the 

 oxyd of uranium : for though the latter sometimes takes a form so 

 nearly approaching to the cube as that the eye cannot perceive any 

 difference, yet such instances are certainly not very common. 



In 1805, I noticed some crystals of the oxyd of uranium on the 

 refuse heaps of Tin Croft mine, which is at the foot of a granitic 

 hill called Carnbrae near Redruth ; the veins of that mine run 



