Quick
Search: 		  
advanced search
 GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help 
Mineralogical Magazine Don't get GSW? Talk to your librarian.
JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Published online 3 September 2009
Mineralogical Magazine; June 2009; v. 73; no. 3; p. 373-384; DOI: 10.1180/minmag.2009.073.3.373
© 2009 Mineralogical Society of Great Britain and Ireland
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Google Scholar
Right arrow Articles by Wiedenmann, D.
Right arrow Articles by Keller, J.

Alumoåkermanite, (Ca,Na)2(Al,Mg,Fe2+)(Si2O7), a new mineral from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, northern Tanzania

D. Wiedenmann1,2,*, A. N. Zaitsev3, S. N. Britvin4, S. V. Krivovichev4 and J. Keller5

1 Department of Geoscience, University of Fribourg, Perolles, 1700 Fribourg, Switzerland
2 EMPA, Swiss Federal Laboratories for Material Testing and Research, Hydrogen and Energy, Ueberlandstrasse 129, Duebendorf 8600, Switzerland
3 Department of Mineralogy, Faculty of Geology, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg 199034, Russia
4 Department of Crystallography, Faculty of Geology, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg 199034, Russia
5 Institut für Geowissenschaften, Mineralogie-Geochemie, Universität Freiburg, Albertstrasse 23b, 79104 Freiburg, Germany

* E-mail: daniel.wiedenmann{at}gmail.com

Alumoåkermanite, (CaNa)2(Al,Mg,Fe2+)(Si2O7), is a new mineral member of the melilite group from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, Tanzania. The mineral occurs as tabular phenocrysts and microphenocrysts in melilite-nephelinitic ashes and lapilli-tuffs. Alumoåkermanite is light brown in colour; it is transparent, with a vitreous lustre and the streak is white. Cleavages or partings are not observed. The mineral is brittle with an uneven fracture. The measured density is 2.96(2) g/cm3. The Mohs hardness is ~4.5-6. Alumoåkermanite is uniaxial (-) with {omega} = 1.635(1) and {epsilon} = 1.624-1.626(1). In a 30 µm thin section (+N), the mineral has a yellow to orange interference colour, straight extinction and positive elongation, and is nonpleochroic. The average chemical formula of the mineral derived from electron microprobe analyses is: (Ca1.48Na0.50Sr0.02K0.01){Sigma}2.01(Al0.44Mg0.30FormulaFormulaMn0.01){Sigma}0.99(Si1.99Al0.01O7). Alumoåkermanite is tetragonal, space group PFormula21m with a = 7.7661(4) Å, c = 5.0297(4) Å, V = 303.4(1) Å3 and Z = 2. The five strongest powder-diffraction lines [d in Å, (I/Io), hkl] are: 3.712, (13), (111); 3.075, (25), (201); 2.859, (100), (211); 2.456, (32), (311); 1.757, (19), (312). Single-crystal structure refinement (R1 = 0.018) revealed structure topology typical of the melilite-group minerals, i.e. tetrahedral [(Al,Mg)(Si2O7)] sheets interleaved with layers of (CaNa) cations. The name reflects the chemical composition of the mineral.

KEYWORDS: alumoåkermanite, åkermanite, melilite, new mineral, volcanic rock, chemical composition, crystal structure, Oldoinyo Lengai, Tanzania






JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2009 by Mineralogical Society of Great Britain and Ireland