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Laachite, (Ca,Mn) (sub 2) Zr (sub 2) Nb (sub 2) TiFeO (sub 14) , a new zirconolite-related mineral from the Eifel volcanic region, Germany

Nikita V. Chukanov, Sergey V. Krivovichev, Anna S. Pakhomova, Igor V. Pekov, Christof Schaefer, Marina F. Vigasina and Konstantin V. Van
Laachite, (Ca,Mn) (sub 2) Zr (sub 2) Nb (sub 2) TiFeO (sub 14) , a new zirconolite-related mineral from the Eifel volcanic region, Germany
European Journal of Mineralogy (March 2014) 26 (1): 103-111

Abstract

The new mineral laachite was discovered in a sanidinite specimen from the Laach Lake (Laacher See) volcano, Eifel region, Rheinland-Pfalz, Germany. Associated minerals are sanidine, allanite-(Ce), baddeleyite, hauyne, hedenbergite, intermediate members of the jacobsite-magnetite series, phlogopite, rhodonite, spessartine, tephroite, thorite, zircon, and a pyrochlore-group mineral. Laachite is deep brownish-red, has an adamantine lustre, and is translucent; the streak is brownish red. It forms long-prismatic crystals up to 0.02 X 0.04 X 0.5 mm, which are present as random intergrowths and twins in cavities within sanidinite. The density calculated from the empirical formula is 5.417 g/cm (super 3) . The mean refractive index calculated from the Gladstone-Dale relationship is 2.26. The Raman spectrum shows the absence of hydrogen-bearing groups. The chemical composition is (electron microprobe, mean of 5 analyses, wt. %): CaO 4.29, MnO 9.42, FeO 5.73, Y (sub 2) O (sub 3) 2.56, La (sub 2) O (sub 3) 2.00, Ce (sub 2) O (sub 3) 6.37, Nd (sub 2) O (sub 3) 2.22, Al (sub 2) O (sub 3) 0.99, ThO (sub 2) 7.75, TiO (sub 2) 10.98, ZrO (sub 2) 19.39, Nb (sub 2) O (sub 5) 27.82, total 99.52. The empirical formula based on 14 O atoms is: (Ca (sub 0.66) Mn (sub 0.37) Th (sub 0.25) Y (sub 0.20) La (sub 0.11) Ce (sub 0.34) Nd (sub 0.11) )(Zr (sub 1. 36) Mn (sub 0.64) )(Nb (sub 1.81) Ti (sub 1.19) )(Fe (sub 0.69) Al (sub 0.17) Mn (sub 0.14) )O (sub 14. 00) . The simplified formula, taking into account the structural data, is: (Ca,Mn) (sub 2) (Zr,Mn) (sub 2) Nb (sub 2) TiFeO (sub 14) . Laachite is monoclinic, space group C2/c, a = 7.3119(5), b = 14.1790(10), c = 10.1700(7) Aa, beta = 90.072(2) degrees , V = 1054.38(1) Aa (super 3) , Z = 4. The crystal structure was solved using single-crystal X-ray diffraction data. Laachite is a monoclinic analogue of zirconolite-3O, CaZrTi (sub 2) O (sub 7) , with Nb dominant over Ti in the octahedral sites Nb1 and Nb2 and Fe dominant in a site with four-fold coordination. The strongest lines of the powder X-ray diffraction pattern [d, Aa (I, %) (hkl)] are: 4.298 (22) (022), 2.967 (100) (20-2, 202), 2.901 (59) (042), 2.551 (32) (15-1, 151, 240, 004), 1.800 (34) (24-4, 244), 1.541 (24) (37-1, 371), 1.535 (23) (20-6, 206), 1.529 (23) (046).


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 26
Serial Issue: 1
Title: Laachite, (Ca,Mn) (sub 2) Zr (sub 2) Nb (sub 2) TiFeO (sub 14) , a new zirconolite-related mineral from the Eifel volcanic region, Germany
Affiliation: Institute of Problems of Chemical Physics, Chernogolovka, Russian Federation
Pages: 103-111
Published: 201403
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 36
Accession Number: 2014-028690
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
N50°23'53" - N50°23'53", E07°17'18" - E07°17'18"
Secondary Affiliation: Saint Petersburg State University, RUS, Russian FederationMoscow State University, RUS, Russian FederationSuedwestdeutsche Salzwerke AG, DEU, GermanyRussian Academy of Sciences, Institute of Experimental Mineralogy, RUS, Russian Federation
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201418
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