Mutual exsolution in hornblende and cummingtonite; compositions, lamellar orientations, and exsolution temperatures

Other| August 01, 1996 Mutual exsolution in hornblende and cummingtonite; compositions, lamellar orientations, and exsolution temperatures Ulrich Klein; Ulrich Klein Albert-Ludwigs-Universitaet, Institut fuer Mineralogie, Petrologie und Geochemie, Freiburg, Federal Republic of Germany Search for other works by this author on: GSW Google Scholar John C. Schumacher; John C. Schumacher Search for other works by this author on: GSW Google Scholar Michael Czank Michael Czank Search for other works by this author on: GSW Google Scholar Author and Article Information Ulrich Klein Albert-Ludwigs-Universitaet, Institut fuer Mineralogie, Petrologie und Geochemie, Freiburg, Federal Republic of Germany John C. Schumacher Michael Czank Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X Copyright © 1996 by the Mineralogical Society of America American Mineralogist (1996) 81 (7-8): 928–939. https://doi.org/10.2138/am-1996-7-815 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Ulrich Klein, John C. Schumacher, Michael Czank; Mutual exsolution in hornblende and cummingtonite; compositions, lamellar orientations, and exsolution temperatures. American Mineralogist 1996;; 81 (7-8): 928–939. doi: https://doi.org/10.2138/am-1996-7-815 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Exsolved pairs of hornblende and cummingtonite from two localities in southern New England, U.S.A., have been studied using transmission electron microscopy (TEM) to measure the crystallographic orientation of the exsolution lamellae. Both the cummingtonite and the hornblende show multiple generations or stages of exsolution. Electron microprobe analyses gave compositions of the pre-exsolved (averages) and the coarsest exsolved amphiboles.In amphiboles, two orientations of lamellae are usually present and nearly parallel to {100} and {101} of the host. The observed lamellar orientations are consistent with orientations predicted by the optimal phase-boundary (OPB) theory and are a function of small differences in a, c, and β of the host and exsolved amphiboles (Δa = ahost - alamella, Δβ = βhost - βlamella, and Δc = chost - clamella). Because these lattice parameters vary with T and composition, the precise orientations of the lamellae are controlled by these variables. The widths of determined exsolution lamellae varied from microscopic (micrometer size) to submicroscopic (nanometer size). The TEM images show, in some cases, multiple generations of lamellae with lamellar orientations near {101} differing up to 4.1°, whereas orientations near {100} differed up to 4°. For two pairs of coexisting amphiboles, the T dependence of the lattice parameters from 25 to 600 °C was measured using a Guinier camera. The OPB calculations indicate that for all the samples the different lamellar generations formed between about 780 and 300 °C (±80 °C, on the basis of maximum errors of the lattice-parameter determinations). Lamellae of the same generation all showed nearly the same width. Exsolution temperatures could not be derived from the “100” lamellae because relatively small variations in Δc, which controls exact orientation of the “100” lamellae, could not be measured accurately enough. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.