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September 1999

Gemstones & Pearls: News

Blue's Brothers

The popularity of tanzanite has ushered in a plethora of simulants

L ook for a synthetic version of the mineral forsterite to create a splash in the U.S. The new material looks like tanzanite, is manufactured in Russia and enters the market at a time when natural tanzanite supplies are falling, prices are rising and demand is surging.


This synthetic forsterite could be misrepresented – accidentally or intentionally – as tanzanite, the blue to purple gem that has taken the country by storm in the past few years. While buying and selling a tanzanite simulant is fine – the products are beautiful and in most cases more durable than tanzanite – you should know what the simulants are so you can tell the difference. And of course you must pass this information on to your customer, preferably in writing. Failing to do so could be chalked up as fraud.


Tanzanite simulants include laboratory-grown forsterite, corundum, garnet, spinel and glass. The emergence of these simulants raises some concern because it's easy for disreputable sellers to mix natural tanzanite parcels with look-alike lab-grown simulants without disclosing that fact. But knowing the physical and optical characteristics of tanzanite and its simulants will help you avoid making a mistake. (Look for ways to separate simulants from gemstones by using gemological filters in the November 1999 issue of Professional Jeweler.) Here's a closer look at the characteristics of tanzanite and its simulants.


Tanzanite
The name conjures up an image of mixed color: blue and purple in varying degrees of saturation, reminiscent of the foothills of Mount Kilimanjaro in the Merelani region of Tanzania, the only place where tanzanite is mined. In the past two years, tanzanite prices have escalated dramatically because of shortages. In sizes over a carat, tanzanite can sell in excess of $1,200 per carat retail. Tanzanite's characteristics are:

  • Refractive index: 1.690-1.700.
  • Specific gravity: 3.35.
  • Hardness: 6-7.
  • Optical: Strongly trichroic, showing strong blue, purplish red and greenish yellow with a dichroscope.

Synthetic Forsterite
This new laboratory-grown material, first shown in the U.S. at the 1999 Tucson gem and mineral shows, comes from the Soviet Union. Forsterite is a form of the mineral olivine (peridot) and is considered rare in nature. Tom Chatham of Chatham Created Gems Inc., San Francisco, CA, says he is considering distributing the material in the United States.


Other potential distributors include the Morion Co. in Brighton, MA, and Martin Haske of Adamas Gemological Laboratories, Brookline, MA, which are showing samples of the material.
Retail prices for cut stones could be as low as $100 per carat.

  • Refractive index: 1.67- 1.651.
  • Specific gravity: 3.217.
  • Hardness: 6.5-7.
  • Optical: Strongly trichroic, showing blue, blue violet and grayish blue.

Synthetic Sapphire
This lab-grown corundum is fine-tuned to look like bluer tanzanite. It's far harder than tanzanite, registering 9 on the Mohs hardness scale. But it lacks tanzanite's and synthetic forsterite's strong pleochroic showing of blue and purple.

The Lannyte Co., based in Houston, TX, manufactures Coranite™, the laboratory-grown stones pictured on the previous pages. Corundum made to look like tanzanite is marketed by other manufacturers under a variety of other names, including Chortanite™.

  • Refractive index: 1.762-1.770.
  • Specific gravity: 4.00.
  • Optical characteristics: Moderate pleochroism with violet and blue.
  • Hardness: 9.

Synthetic Garnet (Tanavyte™)
Lannyte Co. distributes this material. Bob Silverman, owner and CEO, says it's a form of synthetic garnet that favors violet over blue. "Some people prefer tanzanites that are less blue," he says. "This product is for them."
u Refractive index: This material is generally over the limits of the refractometer at 1.833 and above, and it's singly refractive.