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Crystal-chemistry of a complex Mn-bearing alkali amphibole ("tirodite") on the verge of exsolution

Roberta Oberti and Subrata Ghose
Crystal-chemistry of a complex Mn-bearing alkali amphibole ("tirodite") on the verge of exsolution
European Journal of Mineralogy (December 1993) 5 (6): 1153-1160

Abstract

EPMA, ion-probe and Mossbauer analyses combined with XRD structure refinement of a straw-yellow Mn-bearing alkali amphibole from Tirodi, Maharashtra, India, with no evidence of exsolution or inclusions, indicate a composition (Na (sub 0.30) K (sub 0.03) )(Na (sub 0.87) Ca (sub 0.39) Mn (sub 0.57) Mg (sub 0.17) )(Mg (sub 3.84) Fe (super 3+) (sub 0.72) - Mn (sub 0.38) Li (sub 0.06) )(Si (sub 7.88) Al (sub 0.12) )O (sub 22) F (sub 0.40) (OH) (sub 1.60) , nearly half- way between the Ca-Na and Fe-Mg-Mn amphiboles. It has a 9.704, b 17.990, c 5.297 Angstrom, beta 103.51 degrees ; space group C2/m; Z = 2. An (super 57) Fe Mossbauer spectrum shows all the Fe to be trivalent; all Mn is divalent, and preferentially occurs in the split M4' site. The value of the angle beta is related to the M4 cation content, and is consistent with intermediate composition. (super C) Mn (super 2+) is distributed almost equally between the three octahedral sites M1, M2, M3. A small amount of Li is ordered at M3 with concomitant substitution of Fe (super 3+) at the M2 site for charge balance.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 5
Serial Issue: 6
Title: Crystal-chemistry of a complex Mn-bearing alkali amphibole ("tirodite") on the verge of exsolution
Affiliation: Centro di Studio per la Cristallochimica e la Cristallografia, Pavia, Italy
Pages: 1153-1160
Published: 199312
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 24
Accession Number: 1994-001550
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 4 tables
N07°00'00" - N37°00'00", E68°00'00" - E97°00'00"
Secondary Affiliation: University of Washington, USA, United States
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199401
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