DIAMOND.
Diamond
is the hardest mineral on Earth, and this, combined with its
exceptional lusture and brilliant fire, has made it the most
highly prized of all gems. Pure, colourless diamond is the
most popular, but other varieties-from yellow and brown to
green, blue, pink, red, grey, and black- are also found,
depending on the impurities present. Because of the uniform
arrangement of their constituent carbon atoms, diamond
crystals are well-formed - usually octahedral with rounded
edges and slightly convex faces. Their perfect cleavage
facilities the early stages of fashioning but they can only
be polished by other diamonds.
Occurrence
Diamond
forms at high temperature and pressure 80km (50 miles) or
more underground. When India and later Brazil were the main
producers, most diamond came from secondary sources, such as
river gravels. However, since the discovery of diamond in
kimberkite rock in south africa (around 1870), its
extracting has involved processing vast quantities of rock.
Australia is the main producer today; other localities
include Ghana, Sierra Leon, Zaire, Botswana, Namibia, the
former USSR, the usa, and Brazil.
REMARK
Diamonds
are graded by colour, cut, clarity and carat (weight) -the
fourc's.
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DIAMOND
BROOCH
Diamond
and emeralds set in gold make up this birds-
shaped brooch, with pearls top and bottom |
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DIAMOND
CRYSTALS
Cubic habit
uncommon
Sugar-like
surface texture |
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BUTTERFLY
BROOCH
This glittering brooch, set with more than 150
diamonds, shows examples of round, square, drop,
pendeloque, and fancy cuts. |
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CRESCENT
BROOCH
Colourless
diamonds are the most highly prized, in this
brooch, many fine, brilliant-cut examples have
been mounted in gold. |
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