winza ruby? no sorry my name is rhodonite! - gia in … · winza ruby? no sorry, my name is...
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Winza ruby? No sorry, my name is Rhodonite!
Vincent Pardieu GIA Laboratory, Bangkok
Figure 1: A fine faceted rhodonite (around 2 carats) believed to have been mined from Brazil. The stone is hosting some interesting inclusions reminiscent of the curved tubes or hair like inclusions seen in some fine rubies from Winza Tanzania. Stone Courtesy: Nomad’s, Photo: V.Pardieu
Introduction: In June 2008 I met Prof. Hänni at SSEF lab in Basel, Switzerland. He was looking at a stone with his microscope and invited me to have also a look at it: The stone was orangy red and full of curved tubes like or hair like inclusions. Prof Hänni asked me, with a smile: “Vincent, what do you think it is? “. It was a time both on us were working, in our respective labs, on the rubies from the new deposit in Winza, Tanzania (Schwarz, 2008): Gemologists were then surprised to find for the first time in natural rubies some hair like inclusions. I was feeling that there was obviously something wrong with that stone as Henry Hänni would not just show me a normal Winza ruby… I then replied: “Well the inclusions here look very similar the inclusions we can see in some fine Winza rubies.” He then smiled and added: “Yes, I was also thinking that, but when I took the refractive Index of the stone I found 1.72‐1.73… It is not a ruby!” I was amazed and started to think: “1.72‐1.73? What can it be? Prof. Hänni then proudly added:” I identified it as Rhodonite! Isn’t it amazing?” It was! Prof. Hänni said he was planning to write a short publication about this. Then I kept silence for a while, but started to look at rhodonite with some obvious interest. Recently, thanks to people from Nomad’s Company in Bangkok, I had also the chance to see an attractive rhodonite believed to have been mined in Brazil. The stone was presenting similar inclusions as the rhodonite Henry Hänni invited me to look at. In acknowledging the original sighting in Basel and the interest generated; It is with pleasure that I describe here the wonderful 2ct rhodonite I was recently allowed (by Nomad’s Company) to examine in Bangkok and its incredible inclusion scene. Table 1 sets out the main gemological properties of ruby and rhodonite, clearly showing the significant differences between the two materials.
Table 1: the main gemological properties of ruby and rhodonite which usually do not present any difficulty to separate based on gemological properties
Ruby Rhodonite
Refractive Index: 1.76 ‐ 1.77 1.71 ‐ 1.75
Birefringence : 0.008 0.011 to 0.014
Optical Character: U‐ (Uniaxial Negative) B+ (Biaxial Positive)
Chemical composition: Al2O3 CaMg4Si5O15
Crystal System Trigonal Triclinic
Figure 2 to Figure 7 compare rhodonite and its inclusions with the inclusions seen in Winza rubies:
Figure 2: Our rhodonite seen under dark field illumination. Photo: V.Pardieu
Figure 3: Details on the curved tubes inside the 2ct rhodonite using microscope (40x) under dark field illumination. Photo: V.Pardieu
Figure 4: A fine ruby from Winza, Tanzania seen under the same dark field illumination conditions. Photo: V.Pardieu/Gubelin Gem Lab, 2008
Figure 5: Details on the hair like curved tubes seen in a ruby from Winza, Tanzania Photo: V.Pardieu/Gubelin Gem Lab, 2008
Figure 6: Curved tubes and multiphase inclusions in rhodonite. Stone Courtesy: Nomad’s, Photo: V.Pardieu
A good way not to be mistaken is to also to look at the other inclusions present in a given gemstone. In the case of the 2ct rhodonite there were some multiphase orientated inclusions that are not typical of corundum. This unusual inclusion association “for corundum” should raise the suspicions of a trained gemologist. Nevertheless such rhodonite could represent a real identification challenge for people buying stones in the field without a proper set of instruments. This small story is then a perfect study case to remind us that it is all the time better to cross check any observation we have with another gemological instruments in order to validate that observation.
Acknowledgments Thanks are due to Prof. Henry Hänni from SSEF to have shared with the author his observations and to Celine and Mikola from Nomad’s to have given the author the opportunity to study the rhodonite.
References: Schwarz, D., Pardieu, V., Saul, J.M., Schmetzer, K., Laurs, B.M., Giuliani, G., Klemm, L., Malsy, A.‐K, Erel, E., Hauzenberger, C., Du Toit, G., Fallick, A.E., Ohnenstetter, D. (2008) Rubies and Sapphires from Winza. Central Tanzania. Gems & Gemology. 44. 4.
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