Calcareous Genus. 31 



Black. This colour is commonly owing to a 

 flight mixture of Iron. Mr. Bayen found 

 one fpecimen of it to contain five per cent. 

 of iron, yet the lime made of it was at firft 

 white, but in time acquired an ochry* or 

 reddifh yellow colour, 1 1 Roz. 496. 



Mr. Bergman remarks, that all calcareous 

 ftones which grow black or brown by calci- 

 nation, may be fufpefced to contain man- 

 ganefe, in that cafe the lime they form is 

 excellent as a cement. 2 Bergman, 229. 

 And according to Rinman (Hiftory of Iron, 

 189,) white calcareous ftones, that grow 

 black by calcination, contain about ten per 

 cent, of iron. 



Grey. This fort of marble contains left 

 iron, only one or two per cent, according to 

 Mr. Bayen. 



Blue and Green marbles derive their colour 

 from a mixture of fhorl, according to Mr. 

 Rinnan, H'lftoriaferri. 201. 206. 



SPECIES III. 



Combined 'with the Vitriolic Acid. 

 Gypfum, Seknite, Plaifter of Paris. 



This fpecies is of different colours, moftly 

 white or grey, of a lamellar, granular, or 



fibrous 



