A X:o 24) The meltinj»- and boilingjioints of metalloidsulphides. 13 



oi tliis table it is possible to arrange tliese minerals in tlie 

 lollowing tlirec groups: 1 :o minerals formed immcdiately 

 at the earths surface: realgar, auripigment, kermesite; 2:o 

 minerals formed near the surface: realgar, auripigment, anti- 

 monite; 3:o minerals formed at greater depths: tetradymite, 

 guanajuatite, bismuthinite and molybdenite. It will be very 

 interesting to see, as the meltingpoints become known, if 

 it will be possible to arrange the minerals of other mineral- 

 groups into series, which can be divided into similar genetic 

 groups. 



