angular
facets are also seen. (In some cases larger holes of the same
octahedral shape may he observed in the section, as though a crystal
had dropped out during the process of grinding.) Frequently these
hodies seem to have concave faces, viz., as in fig. 32, ii. and hi.;
this, however, is probably only an optical illusion. They sometimes
have a decided yellow colour. They have a high index of refraction, and
a dark rim around them. They are usually isotropic, hut traces of weak
douhle refraction in the centre of one of the crystals have been seen,
a pale bluish colour appearing in certain positions, as if it were a
crystal under strain. 1
took
some of the same rock from which the section was made, and after
pulverizing it, separated the heaviest portion by means of Thouiet's
solution. This was put upon a glass plate with a few drops of water,
and then rubbed with a polished sapphire. The sapphire was clearly
scratched. A photograph of one of these bodies (fig. 33) was taken by a
friend, the supposed diamond lying between three crystals of titanic
iron. Four of these supposed diamonds were seen in a single section of
the rock.
I
am not, however, prepared to state that these bodies are diamonds, not
having been able to isolate them. Several colourless isotropic minerals
appear in the rock, among which a colourless garnet, probably
demantoid, occurs in small crystals and might readily be supposed to be
a diamond.
Mr.
Hedley, of the Colonial Exhibition, from whom I obtained my specimens,
informed me that diamonds have been found in the rock as well as in the
soft decomposed material; but as yet their detection under the
microscope cannot be said to be free from doubt.
