Diamonds may be tested by the aid of sapphire. The true diamond will scratch the sapphire.
The
diamond is found in all colors—white, yellow, orange, red, pink, brown,
green, blue, black, and opalescent. There is a slight difference
between the specific gravity of the Indian, or oriental diamond, and
the Brazilian, and also between the white and colored. Absolutely
colorless stones are not so common as cloudy and faintly colored
specimens. The usual tints are gray, brown, yellow or white; and as
rarities, red, green, blue, and black stones have been found. Diamonds
may be the most perfect reflector of light. It may be as purely
transparent and colorless as a dewdrop, or it may display all the
primary colors. It is highly phosphorescent. Even the blackest of
diamonds are transparent to the X-rays. Neither acid nor alkali will
mar it; no solvent will dissolve it; but if heated to a high
temperature in the presence of oxygen it burns to carbon dioxide. It is
oxidized on heating with potassium dichromate and sulfuric acid. Its
brilliant luster and display of prismatic colors are due to the
property of reflecting and dispersing the light rays, a property
possessed in the highest degree by colorless stones. The specific
gravity ranges from 3.47 to 3.56; generally it is about 3.51.
The
specific gravity or relative density of a mineral is the ratio of its
density to water at 4°C. (3g.2°F). The specific gravity of the diamond
as given by different writers varies considerably, which may be
accounted for by the different conditions under which the experiments
were made, espe-
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