GemSelect Newsletter - August 2010
In our newsletter this month:
African Spessartite Garnet Back to Top
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.
Rare and Unusual Gems Back to Top
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:
Big Clean 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.
Customer Questions Back to Top
Every month we answer questions of general interest from our customers. Please feel free to send your questions or suggestions to our support team at firstname.lastname@example.org!
Can you tell me about the the "asscher cut"? Do you sell any gemstones in this cut? ET, USA.
The asscher cut is actually quite an old style, dating from 1902. But it has become popular again for diamonds and is now starting to be found in colored gemstones. The asscher cut is a square step-cut with truncated corners and a deep, pointed pavilion. You may think of it as a more brilliant version of the emerald-cut, with an octagonal face-up outline and a distinctive windmill effect on the table. For more information on the asscher cut, please see our article on the topic. We have just begun producing some asscher cuts in our workshop and you can see some samples here.
I saw some teal blue gems called amazonite on your website. This is just the color I was looking for. Is amazonite a type of quartz? Thanks for any information. RB, South Africa.
Amazonite looks like it could be a type of chalcedony quartz, but it's actually a form of potassium feldspar, in the same family as moonstone and orthoclase. Like moonstone, it has a hardness of 6 to 6.5 on the Mohs scale. The color is somewhat similar to turquoise and for long time it was believed that amazonite was also colored by copper. But recent studies suggest that the blue-green color results from small quantities of lead and water in the feldspar. Amazonite is found in several locations, but most of the fine material comes from Brazil.
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