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Gem
Criteria
Hardness is a major factor. If a gem is too soft it
will scratch easily and, if its beauty would be rapidly
lost due to abrasion. Some extremely minerals are cut
for collectors and can be thought of as noncommercial
gems. But their lack of durability makes it questionable
if the term "gem" can be applied to them.
Durability combines various characteristics into a general
term that indicates how well a gem wears v use. Objects
such as pearls are not too hard, but hold up well and
retain their beauty for a long time.
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Rarity
is a major factor in evaluating a gem, for much of a
gem's value -e- from its scarcity. The material itself
might be very uncommon. Ur. the other hand, the rarity
of a particular gem might be due to its large size compared
to most other gems of the same material, or its extremely
fine or unusual color. |
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Colors
of paramount importance in a gem. It can make the difference
between $10 and $10,000 per carat in some gemstones. The range
of color to be found in the mineral kingdom is enormous, and
there is great subtlety in the variation of color in a single
mineral species.
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Gem Criteria |
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minerals occur in a wide range of colors, such
as tourmaline, beryl, quartz and spinel. In this
case value is directly linked to the fashion of
the times that is, what color is considered "most
desirable."
Brilliance
and dispersion affect gem value, especially in
the case of colorless materials. Brilliance is
the effect produced by the return of 13 light
from the gem to the eye, and is largely a function
of proper cutting. Dispersion is the optical phenomenon
that creates the color play in diamond.
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High
dispersion is found in only a few stones, but in these it
is responsible for an unusual degree of beauty. Usually brilliance
is sac¬rificed to some degree when a stone is cut for
maximum dispersion, or vice versa. Optimum cutting would maximize
both qualities, hence the search for a set of "ideal"
proportions for cutting diamonds.
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