yellow color centers in cuprian tourmaline

A major factor in the color of gemstones is color centers.  Color centers do not depend on trace amounts of transition elements to produce the color, but by damage to the gemstone’s structure.  The creation of color centers is usually caused by radiation.  The investigation of colors centers in tourmaline is difficult because tourmaline usually contains significant amounts of iron and manganese.  Both elements produce very broad electron  paramagnetic resonance or electron double resonance spectra which causes problem with testing.

Dr. Nassau of the Bell Labs  published an article that indicated that colorless tourmaline could be changed into yellow tourmaline with gamma radiation in 1975.  Sometime ago I found an article that followed up on Dr. Nassau observations.  Its title is  “Investigation of Radiation Induced Yellow Color Tourmaline by Magnetic Resonance.  Its lead researcher is K. Krambrock and it was publish in Nuclear Instruments and Methods in Physics Research 2002.  Any serious technical questions about the investigation of color centers in tourmaline should be directed toward this source.

After making as complete an investigation as I can, I have come to the conclusion that the color center O- is the cause of the color green in a significant amount of Paraiba/paraiba type/ cuprian tourmaline.   I believe that the following facts support my contention.

1,  Copper as a chromophore can not produce anything, but the cyan color in tourmaline.

2,  Some greenish Paraiba/paraiba type/cuprian tourmaline can be heated to produce the cyan color in tourmaline by  eliminating the yellow color originally found to the tourmaline.

3,  Some Paraiba/paraiba type/ cuprian tourmaline have been found to contain extremely low levels of titanium, iron and manganese and still have a greenish color vector.

4.  By the process of elimination, I can not find any other source of a yellow color in tourmaline that would meet the above criteria.

Comments solicited and appreciated.


Again, please consult the research paper for any technical details on what an O- trap is and how it is generated in tourmaline by radiation.


About Bruce Fry

I was born in Summit, NJ in 1947 and graduated from Summit High School in 1966. I graduated from the Colorado School of Mines in 1970 and after spending another year in graduate school, I left to see the world of Brazil. After spending some more time discovering myself, I ended up working for the Commonwealth of Pennsylvania for 32 years as an Air Quality Engineer in the Department of Environmental Protection. I retired in 2007 and took up faceting gemstones again after a long hiatus that reached back to my twenties. I had started cutting cabochons when I was 13 and bought my first faceting machine when I was 15, but ran out of money and time until I retired. My great love in gemology is tourmaline and the collection presented here represents my effort to get as much beauty and variety in the colors of tourmaline as I can. I was particularly lucky in being able to get unheated cuprian tourmaline before copper was discovered in gem grade tourmaline from Mozambique.
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