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: April 2010 Newsletter: Gemstones for Collectors

GemSelect Newsletter - April 2010

In our newsletter this month:
Gemstones for Collectors Back to Top

We're always on the lookout for rare and unusual gem varieties. Since we stock more than 115 different types of colored gems, the rare species on our shopping list are, as you can imagine, rather difficult to find. It takes perseverance and a bit of luck.

We have plenty of perseverance, but last month we had some good luck as well - we were able to add a dozen new gem varieties to our inventory. Here is the news on our latest finds:

One of the rarer gems in the world is known as ammolite. It's a gemstone of organic origin that is fairly new to the market, with commercial mining beginning only in 1981. Ammolite is the fossilized shell of ammonites, which are composed primarily of aragonite, the same mineral that makes up nacreous pearls. Ammolite's main attraction is a remarkable vivid play of color. To date, ammolite has only been found in Southern Alberta in Canada.

Smithsonite is one of two rare zinc-containing minerals discovered by the British chemist and mineralogist James Smithson in 1803. The zinc carbonate is known as hemimorphite while the zinc silicate was named smithsonite in Smithson's honor. Typically blue-green in color, smithsonsite is cut as cabochons. Large clean specimens are especially rare.

Rhodonite is usually rose pink to red with black dendritic inclusions of manganese oxide. Most of the rhodonite you'll find is opaque and cut as cabochons. But there are rare specimens that are pure red, and are sufficiently transparent to facet. They are highly valued by collectors.

Mali garnet is another recent discovery, found in the West African country of Mali in 1994. Mali is a hybrid of grossular and andradite garnets. The presence of andradite is responsible for its superb dispersion or fire, reminiscent of the most famous andradite garnet, demantoid. Mali is still the sole source for this rare garnet.

Dumortierite quartz is an ususual quartz that is integrown with the mineral dumortierite. The inclusions of dumortierite give it a deep blue color that is unique in the quartz world. The color has similarities to lapis lazuli and sodalite, but with the superior hardness of quartz.

Variscite is a rare phosphate mineral from Utah in the USA and looks a bit like a green turquoise. But where turquoise is colored by copper, variscite is colored by chromium. Moldavite is another rare green gemstone, formed from rock vapors resulting from meteorite impacts. To date, moldavite has only been found in the Czech Republic, and is prized by collectors for its rarity and unusual provenance.

Cassiterite is one of the densest materials found in the gemstone world, but translucent specimens are rare. It also has a very high refractive index, higher even than zircon, sphene and demantoid garnet. Calcite is another unusual gemstone. Though it it is quite soft (only 3 on the Mohs scale), it takes an excellent polish and can display very good transparency. It is highly regarded by collectors for its wide range of colors.

Three of the rare varieties we've found are white or colorless gemstones, all with good hardness making them suitable for any kind of jewelry. Goshenite is the colorless form of beryl, the same gem family as emerald and aquamarine. Goshenite was once used for manufacturing eyeglasses and lenses owing to its excellent transparency. Danburite is another hard material (7 to 7.5) with a reasonably high refractive index (similar to tourmaline). Hambergite is unusual in several respects; it has very strong double refraction, with a birefringence rating higher even than zircon; and it is an oddity in the gemstone world in combining a low density with a high refractive index.

Rare and Unusual Gems Back to Top

Each month we feature a rare and unusual gem from our inventory. This month we feature a very rare 3.82 carat ammolite from Alberta, Canada:

Ammolite from Alberta, Canada
Ammolite from Alberta, Canada

Ammolite is the fossilized shell of ammonites, which are composed primarily of aragonite, the same mineral that makes up nacreous pearl. Ammolite is valued for its opal-like play of color, and specimens are evaluated according to the intensity of the colors, and the width of the color spectrum displayed. Our featured stone, which is 25 mm long, is quite unusual in displaying nearly the full spectrum of colors. The ammolite itself is actually a very thin sheet, about 0.5 - 0.8 millimeters in thickness. Ammolite is almost always found in matrix, which is typically a grey to brown shale, chalky clay, or limestone. For this reason ammolite intended for jewelry is always sold as doublets or triplets so it will have the durability to last for many years.

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'm trying to understand blue quartz. I've been offered a piece of jewelry with a beautiful "blue quartz" stone. But I was under the impression that blue quartz is either rare or nonexistent in nature. Is that true? SS, USA.
Answer
Much of what is sold in the market as blue quartz is actually synthetic quartz produced by the hydrothermal method. But there are several kinds of natural blue quartz. There is a rare blue chalcedony, or microcrystalline quartz. Most chalcedony is a lavender color, but there is material from several locations - particularly from Namibia and the Western USA - which is distinctly blue in color.
There is also natural blue quartz which is colored by microscopic inclusions of other minerals, such as fibrous crocidolite or dumortierite. Some of these are nearly as rich a blue as sodalite or lapis lazuli. But you'll find that all of the natural blue quartzes are translucent or opaque, so if you see a highly transparent blue quartz in the market it is very likely one of the synthetic stones.
Question
I saw some very interesting boulder opal on your website? Can you tell me more about it, like how it dfiffers from other kinds of opal? Thanks! BT, USA.
Answer
Boulder opal is the second most valuable type of opal, after black opal. The name derives from the fact that this opal is found embedded in ironstone boulders. The opal usually forms as thin veins within these boulders, and most stones are cut to include some of the host ironstone matrix. Boulder opal is sometimes referred to as "opal in matrix" for this reason. Boulder opal is especially attractive because, like the black opal, it has a dark body tone which adds vibrancy to the play of color. Boulder opal also has a higher density because of the ironstone content, and is more durable as well.

Keep up with our new arrivals before they hit the newsletter by joining our thousands of fans and followers on our social networking pages. We love interacting with our customers - you can visit us on Tumblr, LinkedIn, Twitter, Facebook or Pinterest!

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Happy Gem Hunting!
Your friends at GemSelect

  • First Published: April-01-2010
  • Last Updated: June-29-2017
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Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart