53 



TAB. CCCXXXI. 



ARGILLA electrica. 

 White- Tourmaline. 



This substance, which seems almost new to the whole mi- 

 neralogical world, not being spoken of by any author, was 

 sent me in 1804. It was said to be found in a- mine in 

 St. Justs in Cornwall. I speak of it as new, being really 

 a white Schorl or Tourmaline ; for though Tourmaline is 

 said to occur of all colours included in mixtures of yellow, 

 red and blue, yet it is not mentioned as ever having been 

 found colourless or white until now ; therefore this is the 

 rarest known. It is transparent in the fragments, but is 

 so divided by cracks and flaws in general as to appear of an 

 opaque whiteness in parts. The form of the Crystals 

 agrees with that of Schorl. Their position, lying ex- 

 posed among Quartz Crystals, is rather new, as Tourmaline 

 mostly occurs imbedded in Quartz and Petuntse or Feld- 

 spar. 



The late Hon. Charles Greville, who is much to be la- 

 mented from a loss I particularly sustain in the intimate 

 recourse he allowed me to his specimens, pointed out the 

 idea of my specimen being a white Schorl at the time I 

 first showed it to him; even that recollection adds value to 

 the specimen by putting me in mind of a valuable friend. 

 I never could procure a second specimen, or he would have 

 possessed it. I do not know that he ever procured any. I 

 believe Mr. Herbert, who kindly presented me with this, 

 has one also. 



Among the small Crystals on this specimen is one that 

 most happily shows the primitive on its end almost de- 



