Ruby is red corundum, all other color varieties of corundum being
referred to as sapphire. The ruby color range includes pinkish,
purplish, orangey, and brownish red depending on the chromium and
iron content of the stone. The trace mineral content tends to vary
with the geologic formation which produced the ruby, so original
place designations such as Burmese and Thai have come in later years
to be sometimes used in describing color.
... Most authorities expect a medium to
medium dark color tone in a ruby, naming stones lighter than this,
pink sapphire -- but there is no general agreement exactly where the
line is to be drawn. The old joke about questionable stones goes:
"Whether it's a ruby or a pink sapphire depends on whether you're
the buyer or the seller."
... All corundum gems including ruby
have a long history of enhancement. Unless the seller specifically
states the stone is unheated, you should assume that some kind of
heat treatment has been used. Usually high temperature heating and
controlled cooling is done to clarify the stones, especially by
dissolving "silk" (rutile); but it can also improve tone and
saturation of color. Such treatments can only be detected in stones
whose residual inclusions show signs of heat stress; truly clean
stones will give no clues and cannot be verified as natural color.
The general view at present seems to be that simple heating, being
indistinguishable from Nature's own heating processes, and stable,
is acceptable -- as long as it is disclosed. For this reason such
enhancement does not radically lower the value of ruby gems. Not so
for other more recently invented treatments such as diffusion
coloring, or polymer or glass filling.
... Corundum was first synthesized in
the early 1900's by a simple flame fusion process. Many jewelers and
gemologists have had the unpleasant task of telling the proud heir
that Grandmother's treasured ruby ring or brooch contains a flame
fusion stone and has a lot more sentimental than commercial value.
More complex synthesis processes have been developed in recent
years. These so closely simulate natural formation conditions that
colors and even inclusions look extremely natural and such stones
are difficult for all but the most highly skilled professionals to
identify as man-made.
... Ruby is hard (9) and tough, making
it a superb jewelry stone. (Of course, a heavily included or
fractured stone will be less stable.) For reasonably clean stones,
no special wear or care precautions are necessary. Ruby shows
pleochroism which means that the color varies with the direction of
viewing. Most stones show purplish red and orangey red, although the
presence or absence of trace minerals can dampen either of these.
The overall color can often, but not always, give a clue to a
stone's geographic origin, with Burmese stones tending to purplish
red colors and Thai stones appearing more brownish red. In addition,
many rubies will fluoresce in long or short wave UV and this
property can often be used to help identify a stone's geographic
origin. Burmese rubies often fluoresce so strongly that the effect
is noticeable even in sunlight, such stones seem literally to glow,
and are greatly admired. Thai stones generally lack this property.
Although Asia has historically been the major producer of ruby gems,
there are many other sources including the USA, Australia, and most
...Ruby rough of lower quality is used in
great quantities to make beads, carvings, and other ornamental
objects. The silk, which is so common in corundum, can, if
sufficiently abundant, and precisely arranged, lead to asterism.
With proper cutting, this creates star rubies. Today there are
heating and diffusion processes that can increase the rutile content
and improve such gems. Synthetic star corundums were very popular in
the 1950's under the trade name "Linde Stars" and are still under
... Few other gems have as much myth,
lore and romance surrounding them, with one of the chief attractions
being the protection from misfortune and bad health rubies were
believed to afford their lucky owners. As the science of gemology
developed it became known that many historically important "rubies"
such as the famed Black Prince's Ruby of the British Crown Jewels,
were actually other red gems, most often red spinels.
are the most valuable members of the corundum family. Large gem
quality rubies can be more valuable than comparably sized diamonds
and are certainly rarer. There is a relative abundance of smaller,
(1-3 carat,) blue sapphires compared to the scarcity of even small
gem quality rubies, making even these smaller stones relatively high
... Stones of Burmese origin generally
command the highest prices. The vast majority of rubies are "native
cut" in the country of origin. High value ruby rough is tightly
controlled and rarely makes its way to custom cutters. Occasionally,
such native stones are recut to custom proportions, albeit at a loss
of weight and diameter. Custom cut and recut stones are usually more
per carat, and my own bias is that they are worth it.
... Sinkankas and Miller in the
Standard Catalog of Gem Values, 2nd. Ed. list a wide range of
wholesale prices for faceted gem rubies. Prices are dependent on
origin, color, size, and clarity: from a low of $100 to $15,000/ ct
... Burmese stones in 1/2 to 1 ct sizes
with slightly purplish red color and light inclusions range from
$300 to $3000/ ct, for example. The price survey done by the
International Gem Society reports that clean, top color gems in the
1/2 to 1 ct size range are being sold, retail, on the Internet with
a range of $1000 - $3000/ct.
Facts about Rubies
REFRACTIVE INDEX 1.757 - 1.779
SPECIFIC GRAVITY 3.99 - 4.0
HEAT SENSITIVE No
SPECIAL CARE INSTRUCTIONS None
ENHANCEMENTS Heat treated.
Common. Fractures filled, occasional.