GemSelect Newsletter - August 2010
The gemstone varieties that have been most valued over the centuries are those that combine vivid color with superior hardness and brilliance. This is why ruby, sapphire and emerald were called precious gemstones. But in the modern world of gems there are a few other varieties that many gem traders would add to this exclusive list. Among them is spessartite garnet.
Spessartite (or spessartine) garnet was first discovered in the 1830s in the Spessart Mountains of Bavaria. In the 20th century, it had been mined sporadically in locations such as Sri Lanka, Madagascar and Brazil, mostly along with other gem types. But because production had been limited and unreliable, spessartite was never really marketed.
Prior to the 1990s, spessartite was classified as a rare collector's stone. That changed in 1991 when an important new find was made in Northwestern Namibia. The best Namibian spessartite was such a vivid orange that it was given the name mandarin garnet, a name that is now commonly used for many orange spessartite gems.
The Namibian deposit was soon exhausted but in 1999 a much larger discovery was made in Nigeria. More recently we have seen excellent material coming from Mozambique. Though spessartite is not really plentiful, it currently has reasonable availability, though mining experts warn this is likely to be temporary. Indeed there are persistent rumors that many gem dealers have hoarded spessartite, holding material for the day when supplies are scarce and prices skyrocket.
What makes spessartite garnet so special is its vivid color, outstanding brilliance and the fact that it is always completely untreated.
Spessartite is among the small group of idiochromatic gems, which are colored by a basic element in their composition rather than by impurities. Spessartite is manganese aluminum silicate by composition, and it is manganese that is responsible for the distinctive orange color. A pure manganese spessartite is pure orange, but most specimens have also have traces of iron which result in a rich orange-red color.
Spessartite has the highest refractive index of all the garnet varieties and has a higher refractive index than both sapphire and spinel. It combines this superb brilliance with excellent dispersion (fire).
Pure orange is the most valued spessartite color. Spessartite is rarely found in large sizes. Most stones will display a yellow-orange or red-orange color. All the different colors have their attraction, but specimens with too much brown are less valuable.
When buying spessartite garnet, it is worth keeping in mind the remarkable density of this gemstone, which is denser than even sapphire or zircon. A 6 mm round spessartite will weigh about 1.15 carats. By comparison, a 6 mm round brilliant-cut diamond is about 0.81 carats. So when buying spessartite always check the size of the gem, not just its carat weight.
Each month we feature a rare and unusual gem from our inventory. This month we would like to show you a rare 5.88-carat peridot from Burma:
Peridot is one of the few gem varieties that occurs in just one color - green. That is because peridot, like spessartite garnet, is colored by its basic chemical composition rather than trace impurities. Peridot is magnesium iron silicate by chemical composition, and it is the iron that gives it the green hue. The colors of peridot range from yellow-green to olive-green. The finest peridot comes from Burma, with Pakistan coming a close second. Top colors are rarely found in large sizes, so this 5.88-carat apple-green Burmese peridot is quite unusual. It has remarkable color saturation for a peridot, with minimal brown secondary tones.
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Happy Gem Hunting!
Your friends at GemSelect
- First Published: August-01-2010
- Last Updated: June-29-2017
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