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The Diamond.
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the
author observed a case in which on cleaving one from South Africa, a
small Diamond of almost black colour fell out from its enclosure.
Various included bodies, mostly microscopic, have been recorded by
Brewster, Chatrian, and other observers.
The
surface of a crystal of Diamond is generally smooth ; but it is
sometimes indented with triangular impressions, and in certain cases
is striated with lines parallel to the edges of the octahedral faces.
Some Diamonds present a rough surface, resembling poorly polished
glass, and are not unfrequently dull, as though covered with a thin
coating of gum. These generally cut into very fine white stones.
The Diamond is occasionally found in concretionary crystalline forms, which pass under the name of Bort; while another variety termed Carbonado, of
brownish-black colour, is so indistinctly crystalline as to be often
regarded as compact. These varieties will form the subject of a
separate chapter.
The
Diamond presents a perfect cleavage, parallel to the faces of the
octahedron, which is its primary form. The Diamond cutter avails
himself of his knowledge of this natural structure, and is thereby
enabled in many cases to remove spots from a stone by cleaving, without
resorting to the weary work of grinding. The famous Dr. Wollaston, in
the early part of this century, was one of the first to call attention
to the advantages offered by the ready cleavage of the Diamond. He
purchased one from the firm of Messrs. Rundle & Bridge, which they
considered too much flawed to be worth their while to cut, but the
learned doctor minutely studied the structure of the stone, and having
removed the defective part by cleavage had the perfect portion cut,
when he re-sold it to Messrs.
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