34 Dr. Clarke on a newly discovered Variety [July, 



Article VI. 



Account of a newly discovered Variety of Green Fluor Spar, of 

 very uncommon Beauty, and with remarkable Properties of 

 Colour and Phosphorescence. By Edward Daniel Clarke, 

 LL.D. Professor of Mineralogy in the University of Cam- 

 bridge, Member of the Royal Academy of Sciences at Berlin, 

 &c. in a Letter to the Editor of the Annals of Philosophy . 



(To Dr. Thomson.) 



SIR, 



I avail myself of the first moment of leisure granted at the 

 close of my annual course of lectures in this University, to fulfil 

 my promise of sending to you an account of the Durham Fluor; 

 of which I have received specimens surpassing in magnificence 

 and in the beauty of their crystallizations, any mineral substance 

 I have ever before seen. I am indebted to the Rev. G. Peacock, 

 M. A. Fellow of Trinity College, Cajnhridge, not only for making 

 me acquainted with all the circumstances of the discovery, but 

 also for having had the goodness to procure for me the speci- 

 mens to which I allude. The same gentleman, from notes 

 written upon the spot, has also supplied me with materials for 

 making the present communication. The name of the mine,, 

 whence this singular variety of the fitate of lime has been 

 obtained, is Middlehope Shields; it is the property of Colonel 

 Beaumont ; and it is situate about l£ miles to the north of the 

 village of West Gate, in Weardale, in the county of Durham ; 

 about six miles to the icest of the town of Stanhope. This mine 

 has been worked with great success for a considerable time ; but 

 it was only during three months of the autumn of 1818 that this 

 beautiful mineral was obtained in any considerable abundance. 

 The excavations have since that time been partially interrupted, 

 in consequence of the vein crossing another vein, which is the 

 property of a company of miners, who are known in that county 

 by the name of the London Lead Company. They are now 

 employed in driving a level through the intersecting vein, and in 

 sinking a shaft, for the more effectual ventilation of the mine. 



The rider of the vein (a provincial term designating the sub- 

 stance wherewith the vein is principally filled) is a dark buft- 

 coloured magnesian limestone; sometimes of a very friable 

 texture ; which is accompanied by masses of fluor spar ; some- 

 times cubical, and sometimes amorphous ; of different hues, 

 green, purple, and white ; all of which are not unfrequently exhi- 

 bited in the same mass ; the white occupying the centre, the 

 green appearing towards the external surface, and the purple 

 tinging the intermediate parts ; but it is only in the fats (i. e. 

 large openings or cavities) of what is called the eleven fathom, 



