Ti diffusion in quartz D.J. Cherniak ⁎ , E.B. Watson, D.A. Wark Department of Earth and Environmental Sciences, Science Center 1W19, Rensselaer Polytechnic Institute, 110 8th St., Troy, NY 12180, USA Received 28 April 2006; received in revised form 4 September 2006; accepted 6 September 2006 Editor: P. Deines Abstract We have measured Ti diffusion in quartz under dry 1-atm conditions. Experiments were performed using synthetic and natural quartz and a TiO 2 powder source, with Ti profiles obtained by Rutherford Backscattering Spectrometry (RBS). Over the temperature range 700–1150 °C, the following Arrhenius relation was obtained for diffusion parallel to (001): D Ti ¼ 7  10 -8 expð-273F12kJ mol -1 =RT Þm 2 sec -1 Similar diffusivities were obtained for both synthetic and natural quartz, and for a range of Ti source materials, including natural titanite powder and rutile–quartz single crystal diffusion couples. Although Ti diffusion appears slightly slower in the direction normal to c, this difference is not great. Using these diffusion parameters, calculations indicate that distances over which diffusional alteration of Ti concentrations in quartz could occur in a million years would be on order of 500 μm at 800 °C, and ∼ 15 μm at 600 °C. The Arrhenius relation above should be broadly applicable, and may find application in constraining metamorphic histories under conditions where the Ti-in- quartz geothermometer can be reasonably applied. This relation can also be used to constrain peak temperatures and cooling histories from observations of exsolved rutile needles in quartz and the width of the Ti-depleted zone that develops around the growing needles. Finally, these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz. © 2006 Elsevier B.V. All rights reserved. Keywords: Quartz; Diffusion; Titanium; RBS 1. Introduction Quartz is one of the most abundant minerals in Earth's crust, and occurs as a primary constituent of many rock types. It can contain minor amounts of aluminum, alkalis, and transition elements. Quartz color, and in some cases luminescence, can be attributed to the presence of these elements and the defects they create. For example, tiny rutile needles or TiO 2 in the colloidal state may be responsible for rose and blue quartz coloring, respectively (e.g., Deer et al., 1992). Quartz often reveals detailed records of growth history in fine scaled zoning in individual grains. Some of this zoning is observable by variations in cathodo- luminescence intensity, and correlated with Ti concen- trations. An experimentally calibrated geothermometer utilizing the temperature dependence of Ti solubility in Chemical Geology 236 (2007) 65 – 74 www.elsevier.com/locate/chemgeo ⁎ Corresponding author. Fax: +1 518 276 2012. E-mail address: chernd@rpi.edu (D.J. Cherniak). 0009-2541/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2006.09.001