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The
name “diamond” is a corruption of the
Greek word “adamas” meaning invincible.
Composition
Diamonds
are composed of almost pure carbon.
Crystallography
Diamonds
are the isometric (cubic) form of crystalline carbon as opposed to
the hexagonal form, graphite. Diamonds are the high-pressure
polymorph of carbon and is metastable at room temperature.
Physical
Properties of Diamonds
One
of the most important consequences of the strong bonding of the
diamond crystal lattice is extreme hardness. Diamonds are by far
the hardest of all natural substances and are assigned a hardness
of ten on the Moh scale.
Inclusions
and Birthmarks
Cleavage
cracks and feathery marks often mar the transparency of diamonds,
and these may appear as black spots when seen at an angle such
that light is totally reflected at their surfaces.
Inclusions
are common in diamonds and occur as small crystals enclosed by the
diamond lattice. The most common inclusions are magnesian olivine,
haematite, magnetite, pyrope garnet, enstatite, zircon,
diopside, rutile, pyrrhotite, and liquid carbon dioxide. The pyrope garnet
inclusions are unusually rich in chromium.
Diamond
itself is occasionally found as an inclusion in diamonds, but
graphite is rarely found. Quartz has been found included only in
Brazilian diamonds
Valuation
If
imperfections in the diamond are undetectable under a lens
magnifying ten diameters the diamond is said to be eye (or loupe)
clean, i.e. flawless.
Refer
to the following section for clarity grades: Diamonds>Diamond
Grading>Clarity
Any
inclusion which is visible to the naked eye is sufficient to
detract markedly from the value of the diamond.
Absolutely
Colourless diamonds are very highly prized. Fancy colours in
diamonds are rare being generally faint shades of pink, blue, or
green. Any diamond approaching a deep colour is rare enough to
command a high price.
Apart
from colour and freedom from flaws, the size of a diamond has a
dramatic influence on its value. The price of diamonds increase
very rapidly with increase in size. It is rare for a diamond to
exceed 5 carats in weight and large diamonds are often difficult
to sell as the market for such diamonds is limited.
One
of the most important factors influencing the
value of a gem diamond is the quality and
style of the cutting. Brilliant –cut
diamonds tend to be the most highly valued,
and diamonds improperly cut lose a great deal
of value.
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