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Red spinel
The name spinel may come from the Latin spina
or "thorn," referring to the triangular shape of
the cryste. faces, or from the Greek root spinter, meaning
"spark presumably referring just to the red variety.
Like ruby an and garnet, it has also been called "carbuncle,"
from the Laticarbunculus, or "small coal." However,
recognition that the various types of carbuncle differed in
hardness, led 'their being valued accordingly. Undesirable
confusion habeen created by the alternative name of ruby spinel;
and fact, some of the largest and most famous "rubies"
in the world, such as the "Black Prince's Ruby"
in the English crown jewels, are really spinels, not corundums.
appearance Spinel may be an intense, bright
redlike ruby, but more often tends to be brick red, almost
orang, It can have a violet tinge, and such stones were former
referred to as Balas ruby, after the Badakshan (Balascia)
region of Afghanistan where they were found. The color often
soft: pink, rather than red. Spinel has good luster and transparency.It
is generally given a mixed, oval - round cut; alternatively,
a square or rectangular, step or trap cut.
In earlier times, perfectly octahedral crystals
were used jewelry as they were, uncut, like diamonds. Stones
found as worn pebbles or. irregular pieces were summar rounded
and then polished, like some large spinels now, seen in museums.
Distinctive features Red spinel is fairly similar to ru: the
red color fluoresces slightly in bright light, but much less
than ruby. Being singly refractive, it is not pleochroic.
This feature is in contrast to ruby but in common with garnet,
although the latter is nearly always a rather dull color,
which is not heightened even by strong light. It can be hard
to distinguish splnel from either of these gemstones, in which
case the physical properties will need to be measured.
However, spinel may contain several parallel
rows of minute octahedral crystals of hercynite (iron spinel),
which are highly distinctive and sometimes recognizable with
an ordinary lens. Soft pink varieties can be hard to distinguish
from some tourmalines, although the latter display varying
degrees of birefringence, and have different physical properties.
Occurrence Red and pink spinels
come from the Mogok region of Burma and Afghanistan. Spinels
may also come from Sri Lanka and Thailand, where they are
found together with corundum.
Value As secondary gems go, brilliant red
spinels comparable in color to rubies are quite valuable,
though they are only one-tenth or so the price of rubies themselves.
Pale pink or violet spinels, except for particularly fine
or large specimens, are of much lower value.
Simulants and synthetics Synthetic
spinel in many colors has been widely produced by the flame
fusion method, but owing to difficulties in obtaining the
red variety, the only examples found are extremely rare and
or small size-a maximum of one carat or little more. These
are distinguished from the natural variety by the typical
internal structure and inclusions of gems produced by the
Verneuil method. Recently, synthetic red spinel has also been
produced by the more costly flux melt process, but n has not
proved economical.
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