Trapiche ruby is a single crystal ruby showing textures with six arms and six growth sectors. This structure is well known among jewelry and mineral field after the early works about it [1-3]. There is an important academic work about trapiche ruby, that is based on elemental mapping and optical micrographs [4]. The authors of the paper analyzed their results from the view point of crystal growth. Their discussion and conclusion about the crystal growth process is very interesting. On the other hand, it seems that academic research works about trapiche ruby is not enough yet. We think it is time to accumulate new experimental data about trapiche ruby using updated analytical tools. In this study, we carried out precise experimental analyses and elucidated the microstructure of the trapiche ruby.
The specimens were mined from Myanmar. First, we cut and polished them, then we carried out X-ray pole figure measurements, micro-X-Ray Fluorescence Spectroscopy (XRF), and dispersive X-ray spectroscopy (EDX) mapping with scanning Electron Microscopy (SEM).
Selected experimental results are shown in this paper. We named our specimens shown in this paper as TRu2 and TRu11. Fig. 1 is the results of X-ray pole figure measurements. Bruker's D8-DISCOVER with Cu tube was utilized in this study. These results shows that our specimens are not poly crystals but basically single crystals in case some of them include twin(s).
X-ray pole figures. (a) Taken from the specimen TRu2. It shows a typical pole figure map of single crystal corundum which surface is perpendicular to c-axis. (b) Taken from the specimen TRu11. It shows that the surface is perpendicular to c-axis but this crystal includes twin(s).
Micro XRF mapping results of the specimen TRu2. Fe is localized in the “arm“ area.
Fig. 2 is the results of Micro XRF mapping of the specimen TRu2. HORIBA's XGT-9000 was utilized in this study. The characteristic of this equipment is its micron-order X-ray beam and it enable us to carry out higher space-resolution mapping in comparison with conventional XRF. The experimantal conditions are as follows: Rh-Tube X-ray source (50 kV, 100 μm), vacuum condition (not in the air), 15 µm beam diameter, EDX type X-ray detector. We detected impurities such as Si, S, Ca, Ti, Fe, Cu, Zn other than the main elements of ruby, Al, O, and Cr. It was reveald that Fe is cleary localizen in the “arm“ area.
We also carried out higher magnification elemental mapping using EDX which is equipped with the low vacuum type Field Emission SEM. JEOL's JSM-IT700HR was utilized in this study. This SEM has a low-vaccum mode even though it is a FE-SEM, therefor we can ovserve the oxide specimens without coating so that we can compare optical and SEM images anytime during the operation. We observed the specimen TRu11 with the acclerarion voltage of 15 kV in the air pressure of 30 Pa atmosphere. The resuls of back scattering electron image (BSE), X-ray maps of Al, Cr, Fe, Ca, and S are shown in Fig. 3. This EDX analysys using low-vacuum FE-SEM exhibited precise distribution of these elements. It is obvious that the Fe distribution is identical with the arm area. We need further discussion whether or not other impurities such as Ca and S have same role with Fe to create the arm texture.
Low vacuum type FE-SEM observation and EDX mapping results of the specimen TRu11. Fe is localized in the “arm“ area.
In summary, we conducted precise elemental and crystallographic analysis for the trapiche ruby and it was revealed that the distribution of Fe is identical to the arm area. This main result support previous works reported by other researchers. In the view point of the role of other impurities, further investigation is needed.
