Table of Hardnefs: I 73 



Gypfum, - - 5 - 



Chalk, - 3 - 



Remarks. 



i f * Artificial gems are eafily diftinguiflied 

 from the natural, by their foftnefs, fufibility, 

 folubility in acids, and in many cafes by their 



fpecific gravity. 



d 



2 dly * Stones whofe hardnefs does not exceed 

 1 1 may be fcratched by fteel. 



3 diy - It is remarkable that opal whofe hard- 

 nefs is equal to that of quartz, does not ftrike 

 fire with fteel, as Mr. Bergman attefts, is 

 this owing to its brittlenefs ? but itfeems that 

 opals are of different degrees of hardnefs, 

 for Mr. Quift in a letter to Mr. Rinman, men- 

 tions his having feen opals nearly as hard as- 

 diamond. Mem. Stock. 1766. 



PART 



