Lawsonite; upper pressure stability and formation of higher density hydrous phases

Other| December 01, 1995 Lawsonite: Upper pressure stability and formation of higher density hydrous phases Max W. Schmidt Max W. Schmidt Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, Federal Republic of Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Max W. Schmidt Universitaet Bayreuth, Bayerisches Geoinstitut, Bayreuth, Federal Republic of Germany Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X Copyright © 1995 by the Mineralogical Society of America American Mineralogist (1995) 80 (11-12): 1286–1292. https://doi.org/10.2138/am-1995-11-1218 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 Max W. Schmidt; Lawsonite: Upper pressure stability and formation of higher density hydrous phases. American Mineralogist 1995;; 80 (11-12): 1286–1292. doi: https://doi.org/10.2138/am-1995-11-1218 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 The high-pressure phase relationships in a H2O-saturated synthetic CaO-Al2O3-SiO2-H2O (CASH) system were studied by multi-anvil experiments. The most extreme pressure condition under which pure lawsonite [CaAl2Si2O7(OH)2·H2O] exists is 120 kbar at 960 °C. This maximum stability is located at the intersection of the lawsonite breakdown reaction with the topaz-OH + stishovite = phase "egg" reaction. At lower pressures and higher temperatures lawsonite decomposes to grossular + topaz-OH + stishovite + H2O, whereas at lower pressures and lower temperatures lawsonite first reacts to grossular + phase egg + topaz-OH + H2O and at still lower temperatures to grossular + phase egg + diaspore + H2O. The two latter reactions have positive dP/dT slopes, with lawsonite on the low-pressure side, and thus delimit the occurrence of lawsonite toward higher pressures. The occurrence of topaz-OH (10.7 wt% H2O) is limited through a reaction to phase egg (7.5 wt% H2O) + diaspore; the phase boundary extends from 110 kbar and 720 °C to 130 kbar and 920 °C. Phase egg is inferred to have a composition of AlSiO3(OH) and a monoclinic unit cell similar to that proposed by Eggleton et al. (1978).The high-pressure breakdown of lawsonite in CASH does not result in an anhydrous assemblage. Lawsonite is known to occur experimentally in basaltic and andesitic compositions to at least 77 kbar; however, it is unknown whether topaz-OH and phase egg appear in natural multicomponent systems, in particular those saturated in kyanite and H2O. 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.