Publication details
Crystal-chemical effects of heat treatment on Cr- and V-bearing Ca-dominant green tourmalines (fluor-uvite, magnesio-lucchesiite)
| Authors | |
|---|---|
| Year of publication | 2024 |
| Type | Article in Periodical |
| Magazine / Source | Periodico di Mineralogia |
| MU Faculty or unit | |
| Citation | |
| web | https://doi.org/10.13133/2239-1002/18524 |
| Doi | http://dx.doi.org/10.13133/2239-1002/18524 |
| Keywords | tourmaline; fluor-uvite; magnesio-lucchesiite; heat treatment; structural breakdown |
| Description | We present a detailed study of thermally driven changes in Ca-dominant tourmaline using Electron Probe Microanalysis (EPMA), powder X-ray diffraction (PXRD), Raman and optical absorption spectroscopy (OAS). The KEN samples from Kenya (5 crystal fragments) can be classified as fluor-uvite, while TAN from Tanzania (5 fragments) is dominantly magnesio-lucchesiite. Tourmaline samples were thermally treated in air at 700, 800, 900, and 1000 degrees C. Both sets were green with different hues, TAN with a bluer hue than KEN. After heating, no significant visual changes were observed in TAN samples until breakdown at 1000 degrees C. In KEN, after heating at 700 degrees C, the yellowish tint disappeared. Raman spectroscopy showed no significant changes after heating. Raman luminescence spectra revealed the sharp intensive band located at 680-684 nm, accompanied by a broad band between 690 and 900 nm in all samples heated up to 900 degrees C. OAS spectra look similar, with two major bands in blue and yellow to red regions. In TAN, the bands shift with the increasing Cr/V from 608 to 604 nm. In KEN with low Cr/V, the band is located between 613-617 nm. After heating at 1000 degrees C, both samples broke down with different associations: cordierite/indialite and glass from magnesio-lucchesiite, and cordierite/indialite, mullite-like phase, spinel and glass from fluor-uvite. There was a difference in volume between the samples; both samples expanded in volume, but the KEN sample expanded more with larger pores likely resulting from a higher proportion of volatile phase in this sample. |