293 



SPECIES IL 

 Calciform Ores. 



4. Thefe ores are remarkable for their 

 great weight, their fpecific gravity being 

 from 5,955 to 6,75 : they may be reduced to 

 4 Varieties. 



I. VARIETY^ 



Tin Spar, white Tin Ore* 



5. It is generally of a whitifh or grey CO* 

 lour, fometimes greCnifh or yellowifh, femi- 

 tranfparent and cryftalized in a pyramidical 

 form, or irregularly : it was formerly thought 

 to contain arfenic 5 but Mr. Margraaf found 

 it the pureft of all tin ores, i Margr, 188,, 

 189, though it is faid to contain fometimes a 

 mixture of calcareous earth j its fpecific gra- 

 vity is 6,007* 



II. VARIETY. 

 Opakej broivn or black Tin Ore. 



6. This is alfo cryftalized and imbodied in 

 a ftony matrix of quartz, fluor or mica, or 

 mixed with white or yellow pyrites, or in 

 ores of lead or zinc, cobalt, wifmuth or iron; 

 when thefe cryftals are large, they are called 

 by the Germans zingraupen> and when fmall 



U 3 zin 



