Gemstones & Pearls/News
Something, Over the Rainbow
Theories differ about the true identity
of a mystery material
The question of whether rainbow calsilica occurs naturally or is man-made has gem dealer Bill Heher feeling like his feet are planted firmly in space. In his vast inventory of rare natural gemstones, this is an eye-catching new product. Each piece is unique in its configuration of colors. Heher says jewelry-designers love it.
But what is it? Heher, of Rare Earth Mining Co., Trumbull, CT, says he trusts his supplier when he says the material is mined near Chihuahua, Mexico.
But two labs, SSEF in Basel, Switzerland, and the Gemological Institute of America, Carlsbad, CA, say the material known as rainbow calsilica is man-made colored with man-made pigments. Heher says he trusts them too, but wants to know whos right.
Studying the Studies
In the Winter 2002 Gems & Gemology, GIAs quarterly journal, SSEFs Lore Kiefert and Peter Vandelabeele of Ghent University in Belgium say the rainbow calsilica they studied is a manufactured material. They first saw the material at a June 2002 mineral show in Saint Marie aux Mines, France.
SSEF bought samples to conduct experiments. The dealer selling the samples produced photos of what he said was the mine, as well as studies from a laboratory in Arizona describing the material as a microcrystalline calcite with the color resulting from a copper push that cross-cuts rhyolite.
Kiefert says calcite, unusual pigments and plastic-like material was present in random observations of the stones. Using Raman spectrography, the blue areas were found to be similar to an art-supply pigment, a copper phthalocyamine called PB15. Yellows correlated with commercial pigment PY1, or Hansa yellow. A paraffin-like material also was present in the samples. Kiefert and Vandelabeele say it appeared to have been made from a pulverized carbonate rock mixed with pigments and stabilized with a polymer.
GIA studied samples too. Shane McClure of the GIA Gem Trade Laboratory says GIAs findings coincide with those of the SSEF Lab.
Marty Colbaugh of Colbaugh Processing, Kingman, AZ, imports the material from Mexico in slabs. His company stabilizes it with an epoxy to increase resiliency. Colbaugh gave photos of the mine to Professional Jeweler. I didnt take the photos, he says. They were taken by people allowed in the area. Not being allowed in the area is part of the problem of authentication for me and for geologists. GIA has seen the photos too, but says the images cant prove natural origin.
Colbaugh hired John Roth, a geologist-mineralogist from the University of Illinois at Chicago, to conduct a separate study. While the study remains unfinished at presstime, Roths initial findings do not compare with SSEFs. Roth says his findings using Raman spectroscopy yield different results than SSEFs tests, but says the findings are preliminary.
Whatever the material is, Heher says hes been selling it in great quantities, even after patiently explaining to customers the contrasting theories surrounding its identity.
by Robert Weldon, G.G.
||Rainbow calsilica in a variety of colors but is it natural? Gems are from Rare Earth Mining Co., Trumbull, CT; (203) 378-8627. Photo by Robert Weldon.
||A close-up of the rock wall inside the mine with a vertical blue seam and hammered chunks of material said to be rainbow calsilica. Photo courtesy of Colbaugh Processing.