MINERALOGY OF BLACK LAKE AREA. 
13 
Native Element. 
DIAMOND. 
Microscopic crystals of diamond were obtained from chromite 
of the Montreal pit by R. A. A. Johnston, mineralogist of the Geological 
Survey. The following is his description of the diamonds and the 
method of extraction. 1 
“No. 1. This specimen consisted of a massive, shiny black, some- 
what granular chromite, more or less intimately mixed with some greyish 
serpen tinous material. 
A fragment was broken from this specimen 
and crushed to a powder passing a sieve of 
sixty meshes to the linear inch; this powder 
was, when treated in a separatory tube with 
Thoulet solution , of a specific gravity of about 
3-0; the heavier separate which settled at the 
bottom of the tube weighed after washing and 
drying approximately 11 grammes; this was 
mixed with 50 grammes of chemically pure dry 
carbonate of soda and the mixture fused in a 
large platinum crucible at a cherry red heat for 
four hours; after cooling the melt was digested in 
distilled water to complete disintegration, the 
supernatant liquid filtered off, and the residue 
treated with hydrochloric acid to remove oxides 
of iron, magnesium, etc. About half of the 
chromite was removed in these operations. 
This course of procedure was repeated several 
times. It soon became evident that this method 
was of little effect upon the coarser particles of chromite that were 
being left after each set of operations. Fusion with bisulphate of pot- 
assium was then resorted to, and the residue from this treatment, which 
showed a number of minute diamonds along with some undecomposed 
chromite, was freed from the latter by a final fusion with sodium 
carbonate. 
“The residue of diamonds obtained in the manner indicated above 
was found to weigh nearly 7 milligrammes or 0-06 per cent of the heavy 
separate operated upon, which constituted nearly the whole of the 
specimen. 
“These diamonds appear to the naked eye as nothing more than dust 
particles; under the microscope, however, with a moderate power they 
Figure 2. Diamond ex- 
tracted from chromite col- 
lected at the Montreal 
chrome pit ; the crystals are 
microscopic in size, the one 
shown in the figure being 
enlarged nearly 1,000 dia- 
meters; it exhibits a parallel 
growth of octahedra, a 
feature which has been 
frequently noted in these 
minute crystals. 
) Ibid., pp, 83-84. 
