Contamination makes aluminum oxide a priceless gem

Aluminum oxide or corundum is a commonly available material. However, trace levels of contaminates in the crystal structure of aluminum oxide can result in priceless gems, such as rubies, sapphires, and emeralds. Rubies are corundum with chromium contaminates. It's the chromium that produces the deep red color. Next to diamonds, rubies are the most precious gems. Sapphires come in many different colors: yellow, red, pink, and the more traditional color, blue. The blue color is only possible when titanium and iron are both present in the structure. The gem shown in Figure 1 was labeled a ruby at a gem show.


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Figure 1

However, the X-ray diffraction pattern collected on the Rigaku MiniFlex, shown in Figure 2, matches corundum and the two additional phases that can be found in sapphires, mainly, rutile [TiO2] and Cronstedtite [(Fe2+)2Fe3+(Si,Fe3+O5)(OH)4].

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Figure 2

This gem would be more appropriately called a red sapphire.


The fifth generation MiniFlex is a general purpose X-ray diffractometer that can perform qualitative and quantitative analysis of polycrystalline materials. The MiniFlex is available in two variations. Operating at 600 watts (X-ray tube), the MiniFlex 600 is twice as powerful as other benchtop models, enabling faster analysis and improved overall throughput. Running at 300 watts (X-ray tube), the new MiniFlex 300 does not require an external heat exchanger. Each model is engineered to maximize flexibility in a benchtop package. Read more...

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