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GemSelect Newsletter - September 2010

In our newsletter this month:
Unheated Sapphire from Tanzania
Unheated Sapphire from Tanzania
Unheated Sapphire from Tanzania Back to Top

In the last year we've been listing some unheated sapphire from Tanzania at very attractive prices. Since unheated sapphire is hard to find, not to mention rather expensive, these Tanzanian sapphires have proven to be very popular.

The main limitation with these unheated sapphires is that they have been available only in small sizes, with most pieces weighing under 1 carat. We're now pleased to report that we've found a source for larger stones, and we've just acquired a collection of more than 60 outstanding pieces in weights over 1 carat, with quite a few stones over 2 carats. We've had a number of specimens certified at the AIGS gemological lab in Bangkok to verify that they are unheated.

We have these in both round and octagonal shapes. Round sapphires are perennial favorites because they are easy to set and work well in many different jewelry designs. But rounds can be hard to find because it takes more raw material to cut a round stone, and many cutters will cut an oval instead to preserve carat weight. We've found about 30 round unheated sapphires, ranging in weight from 1 to 1.7 carats. Most of these are brilliant cut, but we also have about a dozen diamond-cut stones.

In addition to rounds, we have a selection of about 30 octagonal, scissor-cut sapphires, in weights between 1.4 and 2.8 carats with sizes ranging from 7 x 5 mm to 8 x 6 mm.

Colors for both shapes are a range of pastel hues, including yellow, orange, green, violet, blue and pink, plus some interesting multicolored round gems. The clarity of these is excellent, with almost every stone graded VVS-VS or VVS.

The pastel colors are of particular interest for those considering sapphire instead of diamond for a special piece of jewelry such as an engagement ring or anniversary gift. Pastel colors have more sparkle and fire than the darker colored sapphires, especially in very clean stones. The superb prices of these stones, ranging from $130 to $250 per carat, make them suitable for any project that requires a high quality untreated gemstone that is hard enough for everyday wear.

Rare and Unusual Gems Back to Top

Each month we focus on a rare and unusual gem from our inventory. This month we feature a very fine 10 carat multicolor tourmaline from Nigeria:

Multicolor Tourmaline from Nigeria
Multicolor Tourmaline from Nigeria

There are many bi-color and multicolor specimens of tourmaline, but you'll rarely see a multicolored stone as pretty as this padparadscha-colored tourmaline from Nigeria. Depending on the viewing angle, this gem displays pink, orange, yellow and green. What makes this stone so unusual is its impressive size - 10.15 carats - and its outstanding clarity. We've graded this gem IF (internally flawless).

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 help@gemselect.com!

Question
I read that the only singly refractive gems are diamond, spinel and garnet. Is that correct? JCK, Belgium.
Answer
Singly refractive gems actually fall into 2 categories - cubic crystals and amorphous gems. Cubic crystals include diamond, spinel and garnet; but also fluorite, boleite, sodalite, pyrite, hackmanite and lapis lazuli in its crystalline form (most lapis is found in aggregate form). Amorphous gems include all the opals, natural glass like obsidian and moldavite, and organic gems such as amber, pearl and ammolite. So there are actually quite a few singly refractive gems. The vast majority of gems are, however, doubly refractive.
Question
I've been advised when buying heated sapphire to buy stones that have only been gently heated. Do your sapphires qualify? PS, USA.
Answer
When sapphire is heat-treated, the purpose is usually to dissolve rutile inclusions. When rutile (titanium dioxide) is dissolved, it has two salutary effects - it improves the clarity of the stone by eliminating cloudiness, and it improves the color by the release of titanium into the sapphire lattice.
But very high temperatures are required to achieve this, since rutile begins to dissolve at temperatures around 1650 degrees centigrade and has a melting point of 1843 degrees centigrade. I don't think anyone could fairly call this "gentle heat". In fact it is in the same temperature range as the ovens used to cremate human remains.
Some gemstones, such as quartz, apatite, zircon and tanzanite are heated at much lower temperatures, ranging from 600 to 1200 degrees centigrade. But even these temperatures are 2 to 4 times higher than the maximum temperature of most kitchen ovens.

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Happy Gem Hunting!
Your friends at GemSelect

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