Testing for Tanzanite
A quick test to see if your "gem" is really a
We discussed the gemological properties of tanzanite and three
of its simulants synthetic forsterite, Coranite
(synthetic corundum) and Tanavyte (synthetic garnet)
in our September 1999 issue (p. 48). We also promised a quick
filter test you can use to help separate tanzanite from simulants.
This month, we fulfill that promise.
This easy, inexpensive test is helpful as an initial separating
tool when examining tanzanite parcels and when buying heated
tanzanite at the source. Secondary gemological tests such
as magnification, determination of refractive index, short-wave
fluorescence and specific gravity are needed on suspicious
The quick test involves the use of an Aqua Filter,® a
$12 filter invented and developed by Hanneman Gemological Instruments,
Poulsbo, WA. The aquamarine filter was designed to separate aquamarine
from similar but less-expensive gems such as topaz.
Here's how it works: Place the stones on a white background
and illuminate with a strong incandescent light. Hanneman says
fluorescent light will yield misleading readings. View the stones
through an aquamarine filter and watch the gems change color.
Certain colors indicate certain gemstones.
Here is a list of colors Hanneman says you'll often see by
looking at certain gemstones through the filter:
Turns blue gray
Turns pinkish orange
Flashes of red, blue and green
What about the new synthetic forsterite that looks similar
to tanzanite? "It turns a bright green with the Aqua Filter®,
" says Martin Haske of Adamas Gemological Laboratories,
Brookline, MA, who sells the Russian-made simulant. Haske performed
several tests at the Tucson gem and mineral shows this year and
was the first to highlight the filter test.
Professional Jeweler decided to submit tanzanite and its simulants
to the test, shown in the first photograph below. See if you
can guess which of the stones are actually tanzanite. Give up?
Look at the second photograph, and the explanation below.
by Robert Weldon, G.G.
Six gemstones photographed with the Hanneman Aqua
Filter® and in incandescent light. Which ones are tanzanite?
The same unfiltered gemstones (from left): synthetic
forsterite, Tanavyte, tanzanite, tanzanite, Coranite
and synthetic forsterite.
Copyright © 1999 by Bond Communications.