Grading and Pricing of Gemstones
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Years ago, the world generally referred to two types of gemstones -- precious
and semiprecious. Diamonds, rubies, emeralds, sapphires (and sometimes opals
and pearls) were considered precious, and all other stones, semiprecious.
Today this distinction is obsolete and meaningless, since poor examples of the
so-called "precious" stones can be bought for just a few dollars per carat, while
fine specimens of so-called "semiprecious" stones such as tsavorite (a green garnet)
or tourmaline (especially Paraiba tourmaline) may sell for thousands of dollars per
carat. Clearly, the old terms are inappropriate in such situations. (Besides,
the term "semiprecious" always seems to have a connotation of "semiworthless" and
seems disrespectful of gemstones that are highly desirable in their right.)
Today, the gem market is roughly divided into two separate domains --
diamonds and colored stones. Even this distinction
is arbitrary and misleading, since many diamonds are colored and
many "colored stones" are not. However, the same basic
principles are involved in grading gemstones of both types.
You have undoubtedly heard of the "4 C's"
-- color, clarity, cut, and carat weight. Organizations
such as the Gemological Institute of America (GIA)
and CIBJO (Confederation Internationale de la Bijouterie,
Joaillerie, Orfevrerie, des diamants, perles, et pierres precieuses
) have well established, widely respected standards for judging
these qualities in diamonds. However, there are no similarly accepted
standards for judging other stones, although several systems enjoy
One major difference between the diamond and colored stone markets
is that the diamond market is largely controlled by one organization
-- De Beers Consolidated Mines. Through their near-monolithic
control of diamond mining and distribution, this company has done
much to create a fairly stable market for diamonds, and relatively
small diamonds are readily available in a wide variety of qualities.
In contrast, most colored stones are mined with more primitive
methods, by much smaller companies, and supplies are much more
variable. Many colored stones are much rarer than diamonds of
comparable size and quality and are often unavailable. A sizeable
deposit of a stone may be discovered and quickly distributed to
the market, only to become scarce again in a couple of years.
Such uneven supply and less regulated distribution often contribute
to wide price variations.
The following general rules apply to all gemstones:
- Vivid, saturated colors are more highly prized than subdued
or grayed-out colors. Deeper colors are more highly prized than
lighter ones, unless the depth of color is so great as to make
the stone appear blackish. The best color for any gemstone should be obvious
from several feet or even several yards away. For example, a ruby should be intensely
red from across a room, and a blue sapphire should be obviously blue, not black. The exception to the rule occurs when
the extremes are desired -- truly colorless diamonds are valued more
highly than those with pale colors, and a truly black diamond would be
worth more than one that is merely dark gray.
- Larger stones are more highly prized than small ones, although
stones too large for use in jewelry tend to have lower per carat
- Gems with fewer and smaller inclusions are more highly prized
than those with more numerous and larger inclusions, unless the
inclusions contribute in a positive manner to the appearance of
the stone. For example, insect inclusions increase the value of
amber. Fine inclusions that cause star
or cat's eye effects increase the value of stones such as
corundum or chrysoberyl. Quartz containing
large included crystals of rutile
or tourmaline is often more valuable
than quartz without. Characteristic "horsetail" inclusions are preferred in
- More durable stones are generally more prized than those of
- Rarer stones are more highly prized than more common varieties.
However, if the stone is so rare that it is essentially unknown
to the general public, its value suffers and it is relegated to
the status of a "collector stone." Stones such as boracite,
childrenite, ekanite, eosphorite, painite, and simpsonite are
extremely rare, attractive, and durable, but they are unlikely
to command prices appropriate to their rarity, because there are fewer
persons aware of them and eager to buy them.
- Well cut stones of good symmetry, attractive design, and fine
polish are more prized than poorly cut stones. Unfortunately,
many higher priced stones, such as ruby
and emerald, are often poorly
cut in order to maximize weight at the expense of appearance.
- Stones of famous provenance are more prized than those lacking
in personal history.
- Pairs or suites of stones matched for color, clarity, and
cut are more highly valued per carat than single stones, especially
if the stones are rare on an individual basis.
- Stones that have been enhanced in color or clarity by artificial
means are worth considerably less than unaltered stones of the
- Some gemstones are occasionally more in demand due to their use by well known personalities
or due to intensive marketing, such as the various television shopping networks. Such increases in
demand are faddish in nature and tend to be fairly short-lived.
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