Naturally occurring ferric iron sanidine from the Leucite Hills lamproite

Other| February 01, 1996 Naturally occurring ferric iron sanidine from the Leucite Hills lamproite Scott M. Kuehner; Scott M. Kuehner University of Washington, Department of Geological Sciences, Seattle, WA, United States Search for other works by this author on: GSW Google Scholar Dave J. Joswiak Dave J. Joswiak Search for other works by this author on: GSW Google Scholar Author and Article Information Scott M. Kuehner University of Washington, Department of Geological Sciences, Seattle, WA, United States Dave J. Joswiak 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 (1-2): 229–237. https://doi.org/10.2138/am-1996-1-228 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 Scott M. Kuehner, Dave J. Joswiak; Naturally occurring ferric iron sanidine from the Leucite Hills lamproite. American Mineralogist 1996;; 81 (1-2): 229–237. doi: https://doi.org/10.2138/am-1996-1-228 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 Sanidine crystals precipitating from lamproitic magmas characteristically contain appreciable amounts of Fe3+. Sanidine grains from the Leucite Hills lamproites (Wyoming) have compositions in which up to 70 mol% of the KAlSi3O8 molecule is replaced by KFe3+Si3Os, thus constituting a new natural feldspar component.Sanidine is among the last phases to crystallize in the groundmass of Leucite Hills lamproites and rarely exceeds 150 (μm in length. Nearly all grains are zoned in Fe, ranging from 2.5 wt% Fe2O3 in the cores to 19.6 wt% Fe2O3 at rims adjacent to quenched glass. The Fe-rich rims are relatively narrow on (010) crystal faces in comparison with (001) faces (maximum width 10 μm), probably reflecting faster- (001) and slower-growing (010) crystallographic directions. A near-perfect correlation is obtained by combining Ti, Mg, and excess Si cations with Fe3+ in tetrahedral substitution for Al. Insufficient numbers of R2+ cations exist to balance the high concentrations of Mg through an R2+Mg2+R−11+R−13+ substitution, suggesting the exchange Mg2+Si4+Al−23+ in 2KAlSi3O8, analogous to that found in synthetic leucite and kalsilite. Selected-area electron diffraction and convergent-beam electron diffraction show that the Fe-rich sanidine rims have a C2/m structure with cell dimensions of a = 8.68 ± 0.15, b = 13.14 ± 0.23, c = 7.31 ± 0.15 Å, α = 90.0 ± 0.54, β = 116.0 ± 0.46, γ = 90.0 ± 0.33°, and a calculated cell volume of 747 ± 21 Å3. These crystallographic data are in very close agreement to those obtained previously for synthetic KFe3+Si3O8. The unusually high concentrations of Fe3+, Ti, and Mg in the sanidine rims are likely the consequence of rapid crystallization during quenching of an unusually Si-and K-rich, yet Al-deficient residual magma. 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.