gems, feldspar, andesine, China, Tibet, Inner Mongolia, copper diffusion, treatments

There has been public conjecture that the red andesine and labradorite gems in the marketplace are not natural, but are instead relatively colorless material that has been diffused with copper in the laboratory to produce the red coloration. The first step in elucidating this situation is to determine whether or not copper can be easily diffused into these plagioclases. To make this determination we conducted a set of experiments from June through October of 2008, using a variety of andesine/labradorite plagioclases. In what follows, the methodology for these experiments and their results are presented. Our general approach for exploratory diffusion experiments is to embed the test samples in a refractory oxide powder that has been doped with the element which we wish to diffuse. The embedded samples are then heated to the maximum temperature consistent with the materials involved and held at that temperature for sufficient time to be able to observe a significant diffusion layer, if one forms.