Calcareous Genus. 23 



SPECIES II. 



Combined 'with the Aerial Acid. 



This fpecies comprehends a great variety 

 of external appearances, the moft remarkable 

 of which are tranfparency and opacity, hence 

 I fhall divide it into two feries, the tranfpa- 

 rent and opake ; all effervefce with acids ; 

 none give fire with fteel ; the chryftalized de- 

 crepitate when heated. 



SERIES I. 

 Tranfparent Spars. 



Thefe are of a lamellar texture, and moftly 

 break or fplit into rhomboidal laminae ; and 

 this ftru&ure is generally called fpathofe, or 

 fparry. They are found cryftallized in va- 

 rious forms, rhomboidal, hexangular, trian- 

 gular, polyangular ; but the moft common is 

 the rhomboidal, of which fort is the Iceland 

 cryftal, which poflefles a double refracting 

 power. 



Their fpecific gravity is generally about 

 2,700, when pure from metallic particles; 

 and they generally contain from 34 to 36 

 per cent, of the aerial acid, from 53 to 55 

 of mere arth, and the remainder water. 

 C 4 Thefe 



