246 Dr T. THOMSON'S Account of the 



The faces of the prism are too rough and uneven to admit the 

 application of the reflecting goniometer. By my measurement 

 with the common goniometer, they gave 110, and 70 for their 

 angles. But Mr BOWER, who probably was in possession of spe- 

 cimens better adapted for examination, states the angles of the 

 prism to be 106 30', and 73 30'. The base of the prism, he 

 says, is inclined on the axis at an angle of 113. In none of the 

 crystals, in my possession, could the inclination of the base be 

 observed at all. 



Colour dark-grey, passing into clove-brown. 



The crystals have a fibrous structure. 



Lustre vitreous. 



Brittle, and easily frangible. 



Translucent on the edges. 



Harder than quartz. It even scratches topaz. 



We found the specific gravity to be 3.1636. But the quanti- 

 ty weighed was only 5.64 grains. Mr BOWER states it at 3.41. 



Infusible before the blowpipe per se, and also with borax. Not 

 acted on by acids. 



5.64 grains of this mineral were subjected to a very careful 

 analysis by Mr THOMAS MUIR. He found the constituents as 

 follows : 



Silica, 38.670 



Alumina, 35.106 



Zirconia, ..... 18.510 



Protoxide of iron, . . 7.216 



99.502 



When the zircon was detected by Mr MUIR, I requested him 

 to subject it to a rigid examination, to be sure that it was nei- 

 ther yttria, nor glucina, nor alumina. This was easily done by 

 means of caustic potash, and sulphuric acid. 



