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Ferromerrillite, Ca (sub 9) NaFe (super 2+) (PO (sub 4) ) (sub 7) , a new mineral from the Martian meteorites, and some insights into merrillite-tuite transformation in shergottites

Sergey N. Britvin, Sergey V. Krivovichev and Thomas Armbruster
Ferromerrillite, Ca (sub 9) NaFe (super 2+) (PO (sub 4) ) (sub 7) , a new mineral from the Martian meteorites, and some insights into merrillite-tuite transformation in shergottites
European Journal of Mineralogy (2015) 28 (1): 125-136

Abstract

Ferromerrillite, ideally Ca (sub 9) NaFe (super 2+) (PO (sub 4) ) (sub 7) , is a new mineral related to the whitlockite group. It occurs as a common accessory phase in several Martian meteorites classified as basaltic and olivine-phyric shergottites. The mineral described herein originates from the two meteorites Shergotty (the type occurrence) and Los Angeles. Ferromerrillite is trigonal, space group R3c; the unit-cell dimensions (single-crystal data) for material from Shergotty and Los Angeles are, respectively: a 10.372(2) and 10.3794(6); c 37.217(13) and 37.129(2) Aa; V 3467(3) and 3464.1(1) Aa (super 3) ; Z=6. The calculated density Dcalc. is 3.11 g/cm (super 3) based on the empirical formula Ca (sub 9.00) (Na (sub 0.60) Ca (sub 0.07) ) (sub Sigma 0.67) (Fe (super 2+) (sub 0.53) Mg (sub 0.40) ) (sub Sigma 0.93) P (sub 7.08) O (sub 28) (Shergotty) and 3.14 g/cm3 for Ca (sub 9.00) (Na (sub 0.49) Ca (sub 0.15) ) (sub Sigma 0.64) (Fe (super 2+) (sub 0.78) Mg (sub 0.23) ) (sub Sigma 1.02) P (sub 7.03) O (sub 28) (Los Angeles). The crystal structure of ferromerrillite from the Los Angeles meteorite was solved and refined to R (sub 1) =0.066 on the basis of 1518 independent reflections with I>2sigma (I). Single-crystal studies reveal that ferromerrilite grains from the two studied shergottites are heavily deformed with an angular mosaicity reaching 7 degrees. The latter imply that the mineral grains experienced a shock event but the impact pressure was not high enough (<23 GPa) for the transformation to tuite, gamma -Ca (sub 3) (PO (sub 4) ) (sub 2) , to occur. Ferromerrillite is colourless, no cleavage was observed, Mohs' hardness is approximately 5. In the immersion liquids, the mineral is colourless and non-pleochroic. It is optically negative, uniaxial to anomalously biaxial with 2V up to (-)20 degrees . Refractive indices are: omega 1.623(1) and 1.624(1), epsilon 1.621(1) and 1.621(1) for Shergotty and Los Angeles material, respectively. The mineral is named as Fe-dominant analogue of merrillite.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 28
Serial Issue: 1
Title: Ferromerrillite, Ca (sub 9) NaFe (super 2+) (PO (sub 4) ) (sub 7) , a new mineral from the Martian meteorites, and some insights into merrillite-tuite transformation in shergottites
Affiliation: Saint Petersburg State University, Institute of Geosciences, Department of Crystallography, St. Petersburg, Russian Federation
Pages: 125-136
Published: 2015
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 69
Accession Number: 2016-016542
Categories: Mineralogy of non-silicatesPetrology of meteorites and tektites
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 9 tables
Secondary Affiliation: University of Bern, CHE, Switzerland
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 201609
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