176 



is softer than Carbonate of Lead, which will scratch it, and 

 with which it has been confounded. It is accompanied by 

 small crystals of dull purplish Cubic Fluor, nearly in form 

 of a line above them ; and Galsena or Sulphuret of Lead on 

 the right, and which is distinguished by its square appear- 

 ance. The whole on opaque Sulphate of Barytes, commonly 

 called Cawk in Derbyshire; and there are some small cry- 

 stals of Carbonate of Lead scattered about it. 



According to Mr. Greville, it was about the year 1785 

 that this curious local substance was found ; and the works 

 being discontinued, there are very few specimens known. 

 The outline or geometrical figure explains the form of the 

 columnar crystal, and agrees nearly with some other spe- 

 cimens which terminate with a flat apex. 



TAB. CCCC. 



I his figure is taken from another crystal in the same col- 

 lection as the last. It is a short prism, and shows the pri- N 

 mitive faces by the parallelism of the conspicuous flaws or 

 fractures. It has also two additional faces on the columnar 

 edges, at 153 d 30' with the primitive. 



One of the specimens in the same collection has very thin 

 tabular crystals similarly modified, set edgewise, and form- 

 ing a group about three quarters of an inch in diameter. 



The geometrical figure shows them with a more length- 

 ened column, forming sixteen columnar faces, besides the 

 eight faces which belong to the octaedron of the whole, 

 with the two ends being regular, and forming a polyedron of 

 26 faces : there are two of the truncated cubical crystals ac-. 

 companying this. 



Analysis by Chenevix. By Klaproth. 



Muriatic Acid .8 8*50 



Carbonic Acid . 6 with a little water 6- 



Oxide of Lead .85 85-50 



99 100* 00 



Spec. Grav. 60-651. 



