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Blue spinel
The blue variety of noble spinel was in the
past much les~ widely known and appreciated than the red variety.
Appearance The finest specimens, though rare, have bright
blue color comparable to that of some sapphires and are very
attractive, lustrous, and transparent. Almost a, pleasing
are equally lustrous light violet-blue stones, re assembling
some sapphires of the same color. Most blue spinels, however,
are a deep, dull color tending to soot. gray, albeit with
a violet tinge; and their luster and transparency are marred
by a touch of cloudiness. These are often cut quite shallow,
in an attempt to lighten the color usually with modest results.
Like sapphires, they are normally given a mixed, oval cut.
Distinctive features Fine blue
spinels are hard to distir guish at first sight from sapphires
of a similar color. The, latter may display clear pleochroism,
but this is not always the case, particularly with medium
to light blue specimen, Hence lack of pleochroism is not a
sure distinction. B. there is a marked variation in density,
which is easy to establish, and the refractive indices are
also difference Cloudy, deep-blue spinels, on the other hand,
are quite distinctive.
Occurrence Blue spinel is mainly
found in the gem gravels of Sri Lanka and, rarely, in Burma.
Value Attractively colored
blue stones, which are rare and not very large, are worth
much the same as the red variety, whereas the fairly common,
cloudy, less attractive stones are very modestly priced.
Simulants and synthetics Like
synthetic ruby, dark-blue synthetic spinel was one of the
first synthetic gems to be manufactured, at the beginning
of the twentieth century Synthetic stones were not intended
to imitate natural spinel, but the much more precious sapphire,
after early unsuccessful attempts to synthesize the latter.
Synthetic spinet was colored by adding cobalt
(in natural sapphire, the coloring agent is iron). As a result,
if one of these stones is exposed to strong, tungsten light,
it emits strange gleams of red fluorescence of a type not
seen ir any other stone, and this can be a valuable aid to
recognition. Light-blue synthetic spinel is also produced
in considerable quantities, to simulate another gem: aquamarine
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