The demantoid is one of the most brilliant gemstones that exist, yet
until recently it was little known except among collectors and
gemstone lovers. Strictly speaking it is a green garnet, or rather
the star of the green garnets. Not without reason does it bear a
name which means 'diamond-like'. The name comes from the Dutch and
makes reference to the outstanding quality of this gem, its
incomparable brilliance and fire. Some gemstone lovers claim that a
demantoid will continue to glow even in the shade.
The demantoid belongs to the large gemstone family of the garnets,
and is actually a variety of the garnet mineral andradite. But it is
more than that: it is the most expensive kind of garnet and one of
the most precious of all gemstones. It is highly esteemed on account
of its rarity coupled with that incredible luminosity. For the
latter, at least, there is a plausible explanation: the demantoid
has an extremely high refraction (refractive index 1.880 to 1.889).
Yet its high dispersion is also remarkable, in other words its
ability to split the light which comes in through the facets and
break it down into all the colours of the rainbow. The demantoid is
a master of this, and does it even better than the diamond.
The spectrum of its colours includes many shades of green, from a
slightly yellowish green to a brownish green with a golden glow.
Particularly precious is a deep emerald green, though this only
occurs very rarely indeed. It is not only fine and unusual, but the
specimens are also mostly small, large ones being extremely rare.
Once cut, only a few stones weigh more than two carats, and most of
them hardly exceed one. And even if you come across one set in a
piece of jewellery, it is always likely to be a small stone.
Favourite stone of Russia's star jeweller
There have been a good many beautiful gems which appeared like
shooting-stars in the fascinating world of gemstones and vanished
from the scene again after only a short time. That indeed is
probably what would have happened to the demantoid ... if a goatherd
had not happened to be going about his business one day in Namibia.
But more of that in a moment.
After its discovery in 1868 in Russia's Ural mountains, the
demantoid rapidly proceeded to become a much desired gemstone.
Comet-like, it scintillated among the finest jeweller's workshops in
Paris, New York and St. Petersburg. First and foremost, Russia's
star jeweller Carl Fabergé adored it for its tremendous brilliance
and loved to incorporate it in his precious objects. But with the
chaos of the First World War, the green star began to fade rapidly.
Now, it made only rare appearances in the gemstone trade, and when
it did so it was mostly incorporated in an item of second-hand
jewellery, or among remnant stocks from the places where it had
originally been found in the Urals. Occasionally demantoids were
found in other parts of the world, for example in the Congo, or in
Korea in 1975, but the quality of these stones was such that they
were suitable for collectors' use only.
The situation changed quite suddenly in the middle of the 1990s,
when a new seam bearing gemstones was discovered in Namibia.
Demantoid was among them.
The story of that discovery reads like a thriller. It is set in the
southern Damara country near the Spitzkoppe, as the 'Matterhorn of
Africa' is also known. The vast, steppe-like country surrenders to
the scorching African sun. Far away on the horizon, the 'black
mountains' lie blurred in the bluish haze. It's a dry, hard country.
Yet for a long, long time it had held an unknown treasure: gemstones!
Millions of years before, liquid magma had shot up from the bowels
of the Earth and solidified shortly before it reached the surface.
In the course of time, the wind and the elements removed the surface
strata until finally only the distinctive granite mountain, the
Spitzkoppe, was left. And the gemstones, that is. No-one had an
inkling of their existence until in December 1996, quite by chance,
a wandering goatherd found a number of crystal-like objects which
seemed to him worthy of attention. When he had shown them around a
bit in a nearby village, the attention of experts was drawn to the
find, and they quickly realised what a treasure was being presented
Meanwhile, the Namibian government has issued concessions for
gemstone mines. The rare gemstones are carefully quarried by hand
from the parent rock. Care is taken to ensure that as little as
possible of the precious raw material is lost.
Why the horsetail influences the value of a demantoid
Demantoids from Namibia come in shades from a vivacious light green
to an intense blue-green. They have a striking brilliance. Thanks to
their hardness of just under 7 on the Mohs Scale, they are well
suited to being used in jewellery. However, they do lack one feature
by which the true demantoid had always been able to be identified
through the microscope: 'horsetail inclusions'. These golden brown
crystal threads of chrysotile, mostly appearing to radiate out from
the centre of the stone, had previously occurred in almost all
demantoids. But - more's the pity - they were missing in the
relatively inclusion-free gems from Namibia. These horsetail
inclusions were not only typical of the demantoid; they could even
increase its value if they were pronounced. That may sound
surprising, since as a rule inclusions, which can impair the
transparency of a gemstone, are not a welcome sight. But with the
demantoid's 'horsetail inclusions' it is a different matter. A
beautiful, well formed inclusion can increase the value of the
gemstone considerably, a good many collectors being prepared to pay
a higher price.
If you are offered a demantoid, it is definitely a good idea to have
a look at it through the gemstone microscope. If the stone comes
from Russia, you may be able to see these fine, fibrous wisps whose
resemblance to the tail of a horse is unmistakable. If that is the
case, you have a definite pointer to its origin. At the same time,
this 'fingerprint of Nature' shows you that you are holding one of
the rarest and most valuable gemstones in your hand. This rarity
will also make itself felt in the price, since a demantoid from
Russia will be valued much more highly than a green garnet from
Namibia, however brilliant the latter may be.