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40 THE MATRIX OF THE DIAMOND
Diamond.—We
have deferred to the last the consideration of the most interesting
mineral in our rock. While the diamond is very difficult to observe in
thin sections, it has been found abundantly in the decomposed portion
of the peridotite. In practice it is obtained by the following process
': The ' blue ground ' is spread out upon the ground and exposed to the
sunshine. After a period, dependent on the original condition of the
rock, it has crumbled to a coarse powder, and is then placed in
rotating washers, and all the lighter material washed away. The residue
of chromic and titanic iron, garnet, pyroxene, &c, among which are
the diamonds, is then picked over by hand, and the diamonds are
separated. The number of diamonds thus obtained is something
extraordinary. It is interesting also to find that they become more
abundant the deeper they are from the surface, and where also the
volcanic action was more intense. Tbey are well crystallised in sharp
octahedrons, also in dodecahedrons, at times. The crystallography of
African diamonds2 has been described by several mineralogists, and it is not to our purpose to enter upon that subject.
Carbonados
and black diamonds are also common, not only in large crystals, but
very abundantly as minute, almost microscopic, crystals. The abundance
of these minute crystals is another proof that they are not enclosures
brought up from some other matrix.
I
feel some hesitation in describing certain small highly refracting
crystals in the thin sections of the rock, which may possibly be
referred to as diamonds. Former attempts to describe microscopic
diamonds in rock sections have not been successful. Thus, Professor
Jeremejew3
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