MINERALOGY. mi 



4. Of an octoedral figure. 



a. Clear, colourlefs. This I have feen 

 in the collection of the mine-mailer 

 Mr. Von Swab. 



SECT. CI. 



Observation on the Fluors, 



There are not yet any probable reafons given, 

 why thefe ilones mould be ranked amongft the 

 calcareous or any other earths j and if I am not 

 quite miflaken in my judgment, they are fo 

 much the more different from the calcareous 

 earth, as they, when melted together with it, pro- 

 duce an effect which never can be afcribed to the 

 alcaline earths ; not to mention, that there is by 

 no method yet known any calcareous fubflance to 

 be extracted from them, nor is there any poffi- 

 bility of decompounding them. 



That which caufes the phofphorefcent light 

 vanifhes in the fire, it being impoflible to collect 

 it : in the prefent ignorance of the nature of this 

 matter, it cannot therefore be afiferted, whether it 

 is one of the conflituent parts necelTary to the 

 compofition of thefe flones, or if, in regard to 

 its fmall quantity, it even deferves any attention. 

 I take it to be a fubtle phlogifton, which being 

 modified in various manners, gives rife to fuel* 

 various colours. 



At mineral works this kind of ilone is very ufe- 

 ful in promoting the fufion of the ores, and is 

 therefore as much valued by the fmelters, as the 

 borax is by the effayers : it has alfo from this 

 quality got the name of fluor^ or flux. 



The refemblance between the coloured fluors, 

 find the compofuions made of glafs, has perhaps 



contributed 



