Paraiba Tourmaline and Gold

Even before copper was discovered in gemstones I supplied the GIA in an effort to understand why the material I had obtained from Mozambique had a reverse alexandrite color change (see Laurellite posts), I was very interested in the causes of color in Paraiba tourmaline.  I was relatively new to the inter net and I was surprised to read over and over again that a study by the German Foundation for Gemstone Research had found levels of gold in Paraiba that were higher than the average concentration found in the earth.  I also wonder why this bit of information merited such importance.   Yes, it would set Paraiba tourmaline apart from other tourmaline, but would physically have no effect on its color or any other significant physical attribute at the levels found.  This is not unique to tourmaline, but is a fundamental property of the electronic configuration of gold.  So when I began to read a mutation on the original report of high levels of gold in Paraiba tourmaline, that stated that gold helped color tourmaline, I had to dig deeper.

The first thing I tried was to contact the German Foundation for Gemstone Research.  I was very surprised to get an immediate responce that was an indignate question.  Who is reporting that?  It was obvious that they did not support the report.  But I needed more support to understand where the gold in Paraiba report came from.  I read two of the original papers on color in Paraiba tourmaline.  An American paper that states gold had been reported to have been found in Paraiba by A group of German researches, but could not verify it.  I then read the German paper, that was based on one piece of Paraiba tourmaline and found no report of gold in there sample of Paraiba tourmaline.

Now why a ground breaking, highly influential, research report would mention the report of gold in Paraiba tourmaline without verifying it and my interest Laurellite (a variety of cuprian Elbaite) lead me to investigate the testing of tourmaline for trace elements.  Tourmaline is very difficult to test with traditional methods because it is for all practical purposes, completely insoluble in acids at  standard temperature and pressures.  This has lead to two methods of preparing tourmaline for analysis.  One is the fusing of the tourmaline with a flux.  The combination can then be dissolved in acid and analyzed.  the second method uses a Teflon bomb and hydrofluoric acid.  The tourmaline and acid is heated in the bomb to high temperatures by a microwave furnace.  After striping out the fluoride ions, the tourmaline solution is analyzed.  Both of these methods have problems with contamination in either the flux or acid and certainly are expensive to do with the many careful steps that need to be performed.

More direct methods of analysis have been developed over the years.  The use of xrays can now be used without the need of for disolving the tourmaline to analyze for all concentration of elements in tourmaline if the properly calibrated canals have been set up.  This method and others are beginning to take a back seat to a relatively new kid on the block.  It is called LA-ICP-MS. which stands for Laser Ablation Induction Coupled Mass Spectrometer.  This method permits the formation of a charged gas that can be separated by a   different electrical attraction for each ion, into it individual elements.   This method of analysis has its calibration problems as well, but when done well, it gives quantitative data on most elements in the periodic tables.  The exclusivity of the testing is important, along with its accuracy in measuring of very low levels of the trace elements because you find out information on elements you may have not expected to find or have interest in and therefor not set up to analyze for them.

Since the time frame that would have covered the reporting of the gold in Paraiba tourmaline and the two early papers on color in Paraiba tourmaline, a large number of LA-ICP-MA tests have been performed on cuprian tourmaline.  I use the generic nomenclature here because Paraiba tourmaline is only a small subset of the tourmaline that is copper bearing.  This testing has been preformed, in part to build libraries of data sets to distinguish Paraiba tourmaline from Paraiba like tourmaline from Mozambique and Nigeria.  In all this testing with an advance method that is extremely good at preventing contamination, no level of gold has been reported in any cuprian tourmaline, which of course includes Paraiba.  Any clear unequivocal difference that Paraiba tourmaline may have from the rest of the cuprian tourmaline world , and there are subtle differences, would have been loudly reported because literally millions of dollars have been spent looking that very key to keeping Paraiba tourmaline more highly valued and distinguishable, even in lower grades of material.

So to sum up.  The German foundation that was reported to have found gold in Paraiba denies it.  The only scientific paper that I can find and I have looked with help from a friend in academia, makes only a unverfied reference to finding gold in Paraiba while the final referenced report does not included anything about gold in Paraiba.  This early work has been followed up with a massive amount of highly accurate inclusive testing of all sources of cuprian tourmaline including Paraiba without one single report of gold in the tourmaline samples tested.  And gold could not influence color even if it was present based on universal physical laws.  No gold in Paraiba, Truth in Tourmaline!

A final personal observation.  I am cynical of much of the trades promotions, but when it comes to high quality copper bearing tourmaline, its beauty speaks louder than anything they have come up with.  Unfortunately color is not the key and that will be the next installment on Truth in Tourmaline.

Bruce