248 Dr T. THOMSON'S Account of the 



Easily scratched by the knife ; but not by calcareous spar. 



Opaque, or only translucent on the edges. 



Specific gravity 3.2014. 



Infusible per se before the blowpipe. With carbonate of soda 

 it fuses with effervescence into a dark glass. Fuses with borax 

 and with biphosphate of soda into a black glass, showing the pre- 

 sence of much iron and manganese. 



It was analysed by Mr THOMAS MUIR, who found the consti- 

 tuents to be 



Silica, ...... 56.543 



Protoxide of iron, . . 21.669 

 Protoxide of manganese, 7.802 



Soda, . 8.439 



Driven off by red heat, . 3.178 



97.631 



As the loss in this analysis amounted to almost 2.5 per cent., 

 I requested Mr MUIR to examine the mineral for fluoric acid 

 and phosphoric acid ; but no traces of either of them could be 

 found. If we suppose the loss of weight to be soda, the chemi- 

 cal constitution of Cummingtonite will be 



9 atoms tersilicate of iron, 



3 atoms tersilicate of manganese, 



5 atoms tersilicate of soda. 



If the mineral contain no more soda than was found by Mr 

 MUIR, it will be composed of 



3 atoms of tersilicate of iron and manganese, 

 1 atom tersilicate of soda. 



I think it most likely that this last view is the nearest the truth. 



