Phosphorus-rich topaz from fractionated granites (Podles , Czech Republic)

• Published in: Mineralogy and petrology 2004-06, Vol.81 (3-4), p.235-247
• Main Authors: Kronz, A., Breiter, K.
• Format: Article
• Language: English
• Subjects: Crystals; Granite; Luminescence; Minerals; Phosphorus; Precious stones; Rocks; Transition zone
• ISSN: 0930-0708; 1438-1168
• DOI: 10.1007/s00710-004-0036-6

A detailed electron microprobe study of P, F, Ge and Ga-contents in rock-forming topaz was performed on a suite of Variscan granites at Podlesi in the western Krusne Hory Mts., Czech Republic. Topaz crystals from the relatively less evolved biotite- and protolithionite granites display homogeneous cathodo-luminescence (CL) intensities, whereas topaz from the marginal pegmatite, highly fractionated zinnwaldite granite and greisens show intense oscillatory zoning. Phosphorus contents reach 1.15 wt% P 2 O 5 in topaz from the zinnwaldite granite. Many topaz crystals are distinctly zoned with a maximum P content in the transition zone between core and rim. Phosphorus is incorporated into the topaz lattice by berlinite substitution: Al 3+ + P 5+ = Si 4+ + Si 4+ . The majority of analysed topazes are highly saturated in F, reaching 90-97% of the theoretical maximum saturation. Topaz from the marginal pegmatite only reaches 87-90% of F-saturation. There is a positive correlation between P topaz and P whole rock , but no correlation between F topaz and F whole rock . No difference has been found in P and F contents between magmatic and the hydrothermal (=greisen stage) topaz. Contents of Ge and Ga vary from around the detection limit (approximately 50 ppm) up to 200 ppm Ge and 100 ppm Ga, respectively. [PUBLICATION ABSTRACT]