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Co^iileum. It is of a blue Colour, veined 

 and ipotted with white and yellow, not 

 difficult to imitate by Art ^ but the ge- 

 nuine good Stone fhould refifl Fire and 

 Smoke, and come forth with new Luftre ; 

 of this is made Ultramarine. It is found 

 in Mines of Gold, Silver, and Copper, and 

 more frequently in Pits of Marble, which 

 laft is the Kind generally ufed. 



We next come to a great Number of 

 Specimens of precious Stones of all Kinds, 

 opake and tranfparent, rough and polifhed, 

 fome loofe, others fet. I fhall give my 

 Reader a few Remarks on the Nature of 

 fome of them and begin with the 



Opal^ fuppofed to be the Pyropus of 

 Ovid', this is the fofteft of all Gems, ge- 

 nerally from the Size of a fmall Pea to a 

 Horfe-bean, but fometimes larger than 

 the Bean, and often fmaller than the Pea : 

 Its Colour is whitifh, or rather that of the 

 finefl Mother of Pearl, but fo tranfparent 

 that one may fee deep into the Stone : It 

 is not eafy by Defcription to give an Idea 



of 



