196 
fHE GEOLOGIST. 
or some parts of that neighbourhood, and the very shght 
resemblance between its internal characters and those of any 
other mineral with which we are acquainted, are sufficient 
reasons for establishing its distinction. 
It is found in small flat discs — one to two millimetres in 
diameter, and rarely (if any) more than half a millimetre in 
thickness. These discs are always so firmly set in the 
argillaceous slaty matrix in which they are found, that we 
have never yet been enabled to detach any sufficiently 
perfect to enable us to determine the exact form — they 
evidently belong to an hexagonal prism or very angulated 
rhomboid. The colour is greyish black with a shade of green, 
this is visible in the small translucent fragments ; the dust, 
when pounded, is of a pale green. 
The only clearness observable is in the horizontal direction 
parallel to the base of the small discs — the fracture is slightly 
conchoidal, and in other respects the fracture is unequal. 
It scratches glass slightly. 
The specific gravity is 4.40. 
This mineral disengages a small quantity of water when 
tested in a closed tube. On exposure to heat the angular 
points disappear, and a black globule is formed. With 
borax, it dissolves slowly ; with carbonate of soda or platina- 
foil, the presence of manganese is prominently visible. 
The powder is soluble in heated sulphuric acid only. 
The following are two analyses made by Mr. Damour. 
1st. Silica . . 0-4352 
Alumina . 0*2389 
Ferric Acid 0*1681 
Manganic Acid 0*0803 
Water . 0*0563 
Oxygen. 
0*2260 
0*1115 
Proportion. 
4 
2 
1 
0*0500 
1 
0*9788 
