GETTING "BURNED" WITH FIRE OPAL
by Edna B. Anthony, Gemologist
Using the loupe to
examine gemstones is not one of my strengths. This weakness caused me considerable
embarrassment following the September 1996 Denver Gem and Mineral Show.
During negotiations for the purchase of some nice tanzanites and a beautiful
red spinel, the vendor brought forth a parcel of fire opals purported to
originate from a new source in Mexico.
The colors of the fire opals were
truly lovely. I chose an especially bright reddish orange trilliant cut
and a deep rich "cherry" red marquise to complete the transaction.
Several days elapsed
before I began the usual gemological confirmation tests of each gem I acquired
at the show. The polariscope soon revealed the expected singly refractive
nature of both "opals", but I was in for a shock when I placed the "cherry"
red one under the microscope. Prominent doughnut shaped bubbles glowed
amid syrup-like swirl marks inside the stone.
showed a refractive index reading of 1.52, a much higher reading than the
usual 1.42 to 1.43 for Mexican fire opal. The density also deviated from
the normal range of 1.99 to 2.25 for the red-orange variety. The stone
sank in 2.57 heavy liquid and floated in 2.62.
The trilliant cut
exhibited properties abnormal for opal as well. A refractive index reading
of 1.53 and a specific gravity between 2.62 and 2.67 indicated a paste
(glass) simulant. All doubt vanished when both stones were immersed in
alcohol. This final test disclosed the presence of a distinct layer of
color between the colorless crowns and pavilions. I had, indeed, been "burned"
with triplet imitations of Mexican fire opal!
Naturally, I returned
them to the vendor. He confirmed through GIA testing that the lot had been
"salted" with a number of additional imitations. Shortly afterward, Nancy
Attaway provided me with an excellent specimen of natural Mexican fire
opal, along with a copy of a report from GEMOLOGY WORLD published by the
Canadian Institute of Gemology.
Dated August 8, 1995,
the report stated that the GIA Gem Trade Laboratory issued an alert concerning
two stones purchased in Mexico that had been submitted for identification.
Of particular interest here was that a chemical analysis revealed the presence
of selenium in the imitations. Cadmium sulfo selenide and cadmium selenide
are known agents used to produce the red-orange "selenium glass". The report
described the specimens as "a transparent red that might easily be mistaken
for high quality `cherry' opal", and a "slightly less transparent orange
resembling much of the "Mexican" opal seen in the gem trade".
It seems we are encountering many
more very good synthetics and imitations of the inexpensive gemstones in
the market, as well as those for the expensive ones. This episode emphasizes
the need for increased vigilance to protect ourselves and our clients.
The erosion of customer confidence poses a very real danger to all of us
in our profession if we do not maintain our integrity with full disclosure
(Editors Note: We
wholeheartedly agree with Edna regarding full disclosure of the merchandise
we sell. We all depend upon our vendors for proper identification of gemstones,
whether rough or cut, as well as valid information on their point of origin.
Honesty is the best policy when dealing with our customers. We expect the
same treatment from our vendors.)