a 
404 T. W. E. DAVID, W. F. SMEETH, AND J. A. WATT. 
rock. In some cases the central portions of the blocks are more 
decomposed than the external, and exhibit very clearly the 
granular structure of the rock. 
Some of the chromite-bearing fragments, which are much 
decomposed, are rusty-brown in colour mottled with green, the 
former tint being due to the conversion of the iron pyrites into 
hydrated ferric oxide. 
In one fragment, the black particles of chromite appear to be 
agoregated in parallel bands. Some of the fragments are coated 
with a thin layer of calcite, and the same mineral is found travers- 
ing the rock in the form of minute veins formed by segregation 
or infiltration. 
Hardness.—The undecomposed portions of the rock, which are 
chifly felspar, can be scratched with a steel penknife only with 
great difficulty, and the hardness must be nearly 7. The chromite 
has a hardness of between 5 and 6, and the green mineral a hard- 
ness of about 3. 
Specific Gravity.—The specific gravity of the less decomposed 
fragments comparatively free from the green mineral and from 
diallage, but comparatively rich in chromite, was found to be 2:92, 
while that of a more decomposed fragment containing less chromite 
and more of the green mineral was found to be 2°76. The specific 
gravity, therefore, decreases in proportion to the extent of the 
decomposition. The specific gravity of the felspar approaches 
that of anorthite, being about 2-7, and that of the green mineral 
is slightly less, while the specific gravity of the diallage is about 3. 
In structure the rock is crystalline granular, felspar predomin- 
ating and forming the grey coloured areas. ‘The chromite occurs 
in grains from +4; of an inch up to as much as ¢ of an inch in 
diameter. The diallage crystals are about half an inch in longest 
diameter, and the green patches representing the decomposed 
diallage are approximately of the same size, but show a tendency 
to become blended with one another owing to the spreading of the 
colouring ingredient. The iron pyrites for the most part is of 
microscopic dimensions. 
