OCCURRENCE OF A CHROMITE-BEARING ROCK IN BASALT. 405 
Blowpipe characters.—The diallage is slightly fusible and reacts 
strongly for chromium in the borax head. The green mineral 
also reacts strongly for chromium. The chromite was found to be 
almost infusible except at the ends of very thin splinters. The 
felspar is slightly fusible, and tested by Szabo’s method did not 
give any potash reaction. From this circumstance, taken in 
conjunction with the fact that the rock effervesces somewhat 
briskly in hydrochloric acid, and that the specific gravity of the 
mineral approaches that of anorthite, it is probable that the 
felspar belongs to the lime or lime-soda series. 
Microscopic Structure. 
Thin sections of this rock when viewed under the microscope 
have shown it to bea holocrystalline granular aggregate of felspar 
and chromite, with iron pyrites and a greenish mineral, the green 
colouration of which is due to the presence of chromium. 
Constituents.—The felspar, which is greyish-white to colourless, 
and belongs probably to the lime-soda series, is present in the 
form of granular particles with polygonal outline, which are either 
traversed by numerous irregular cracks, such as are common in 
the felspars of troctolite, or show a zig-zag banding probably pro- 
duced later than the formation of the felspar. The felspars 
especially those which exhibit the zig-zag banded structure, include 
a fine dust of iron pyrites, which is frequently disposed in layers 
following the banding. In some cases curious dendritic forms, 
resembling cabbage-stalks, of iron pyrites bisect the angles of the 
folds. 
The chromite appears in thin sections as more or less translu- 
cent reddish-brown grains of irregular outline, having a very high 
index of refraction. These seem to occupy a central position from 
which radiate out in all directions lines which represent the edges 
of the felspar granules. The crystals are traversed by irregular 
cracks, no true cleavage planes being present. 
The green particles, which seem to represent some decomposition 
mineral containing chromium, are of a dull pale green colour, and 
