Ertl, Andreas and Rossman, George R. and Hughes, John M. and London, David and Wang, Ying and O'Leary, Julie A. and Dyar, M. Darby and Prowatke, Stefan and Ludwig, Thomas and Tillmanns, Ekkehart (2010) Tourmaline of the elbaite-schorl series from the Himalaya Mine, Mesa Grande, California: A detailed investigation. American Mineralogist, 95 (1). pp. 24-40. ISSN 0003-004X http://resolver.caltech.edu/CaltechAUTHORS:20100201-115113213
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Chemical, structural, infrared, optical, and Mössbauer spectroscopic data were obtained on tourmalines from gem pockets in the Himalaya mine, San Diego County, California, including a strongly color-zoned crystal. Calcium and Li abundances increase from core to rim, whereas Mn^(2+) and F increase, reach a maximum, and then decrease. Upon initiation of crystallization of lepidolite, F contents in tourmaline decrease. The black core is a Mn-bearing "oxy-schorl." The grayish-yellow, intermediate zone is Mn-rich "fluor-elbaite" that contains a relatively high Mn content with ~6 wt% MnO. The nearly colorless "fluor-elbaite" rim has the highest Li content of all zones. There is an inverse correlation between the lattice parameter a (for values ≥ 15.84 Å) and the Li content (r^2 = 0.96). Mössbauer studies from the different zones within this crystal show that the Fe^(3+)/Fe(total) ratio increases continuously from the Fe-rich core to the Fe-poor near-rim zone, consistent with increasing oxygen fugacity during pegmatite pocket evolution. There is a high positive correlation between lattice parameter a (for values ≥ 15.84 Å) and (Fe^(2+) + Mn^(2+)) content in tourmalines from the elbaite-schorl series (r^2 = 0.99). Values lower than 15.84 Å for a are likely a consequence of greater ^()B contents in samples that usually have a (Fe^(2+) + Mn^(2+)) content of <0.1 apfu. Positive correlations between Al at the Y site and ^()B (r^2 = 0.93), and between (Mn^(2+) + Fe^(2+)) and ^()Al (r^2 = 0.99) were found in tourmalines from the Himalaya Mine. These correlations indicate that, in the short-range order configurations, YAl is coupled with ^()B, whereas Mn^(2+) and Fe^(2+) are coupled with ^()Al. To obtain the most accurate OH data, different analytical methods were used: SIMS, hydrogen manometry, continuous-flow mass spectrometry, and IR overtone spectroscopy. Some elbaites contain a mixed occupation of F, OH, and O at the W site. Based on these data, the assumption OH = 4 – F appears to be valid only for elbaitic tourmalines with FeO+MnO < 8 wt%. In terms of the conditions of formation, whether gel or glass, the transition from low to high viscosity of the pocket-forming medium occurs before primary crystallization within the pockets ceased. At the pocket stage, Li contents of residual hydrosilicate melt were evidently high enough to promote a continuous transition from schorl-foitite at the pegmatite margin to elbaite-rossmanite-liddicoatite in the final stages of consolidation of the pegmatite interior.
|Additional Information:||© 2010 Mineralogical Society of America. Manuscript received April 14, 2009; manuscript accepted September 3, 2009; manuscript handled by Darrell Henry. Samples from the Himalaya Mine and collecting permissions at the mine were provided by William F. larson, Fallbrook, California. William B. Simmons Jr., University of New Orleans, loaned pink elbaite sample SS4. Special thanks are due to Kurt Ferguson for the H2O determination by macro thermal-extraction. We are grateful to Bernd Marler and Sandra Grabowski, Bochum, Germany, who provided the nMr measurements. We thank A. Wagner, Vienna, Austria, for sample preparation work. We sincerely thank Frank C. Hawthorne, Christine Clark, and Darrell J. Henry for their careful reviews of the manuscript. This work was supported in part by Österreichischer Fonds zur Förderung der wissenschaftlichen Forschung (FWF) project no. AP2050921, by National Science Foundation (U.S.A) grants EAR-0337736 and EAR-0337816 to G.R.R. and EAR-0003201 to J.M.H.|
|Subject Keywords:||Tourmaline; elbaite; schorl; crystal structure; Himalaya Mine; Mesa Grande; spectroscopy|
|Official Citation:||Ertl, Andreas, Rossman, George R., Hughes, John M., London, David, Wang, Ying, O'Leary, Julie A., Dyar, M. Darby, Prowatke, Stefan, Ludwig, Thomas, Tillmanns, Ekkehart Tourmaline of the elbaite-schorl series from the Himalaya Mine, Mesa Grande, California: A detailed investigation American Mineralogist 2010 95: 24-40|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||04 Feb 2010 22:55|
|Last Modified:||26 Dec 2012 11:44|
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