Gemstones & Pearls: News
The popularity of tanzanite has ushered in a plethora of
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.
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.
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
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
- 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.
- Specific gravity: 4.50 to 4.60.
- Hardness: 8.5.
- Optical: Because synthetic garnet is singly refractive, the
stones do not exhibit as diffuse (or soft) an appearance as synthetic
forsterite or synthetic corundum. These stones are also not dichroic
by Robert Weldon, G.G.
|Top: A trio of tanzanite
simulants (from left): a Coranite trilliant cut courtesy
of Lannyte Co., Houston, TX, (800) 248-7959; a Tanavyte
oval courtesy of Lannyte Co.; and a cushion-cut Russian-grown
forsterite courtesy of Chatham Created Gems Inc., San Francisco,
CA, (800) 221-4576.
|Above: Tanzanites like this
have grown in popularity but supplies are down, widening the
opportunity for simulants. This tanzanite was faceted by David
Brackna, Germantown MD.
Copyright © 1999 by Bond Communications.