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GEOREF RECORD

Tinzenite, a member of the axinite group with formula revised to Ca (sub 2) Mn (sub 4) (super 2+) Al (sub 4) [B (sub 2) Si (sub 8) O (sub 30) ](OH) (sub 2)

Edward S. Grew
Tinzenite, a member of the axinite group with formula revised to Ca (sub 2) Mn (sub 4) (super 2+) Al (sub 4) [B (sub 2) Si (sub 8) O (sub 30) ](OH) (sub 2)
European Journal of Mineralogy (February 2018) 30 (1): 177-182

Abstract

The official International Mineralogical Association (IMA) list of minerals had given the formula for the tinzenite, an axinite-group mineral, as Ca (sub 6) Al (sub 4) [B (sub 2) Si (sub 8) O (sub 30) ](OH) (sub 2) . However, this formula does not correspond to compositions reported for tinzenite, which contain less Ca than the other three members of the axinite group, and significantly more Mn (super 2+) than the Mn end member, axinite-(Mn), Ca (sub 4) Mn (sub 2) Al (sub 4) [B (sub 2) Si (sub 8) O (sub 30) ](OH) (sub 2) . Revision of the tinzenite formula to Ca (sub 2) Mn (super 2+) (sub 4) Al (sub 4) [B (sub 2) Si (sub 8) O (sub 30) ](OH) (sub 2) was accepted by the IMA Commission on New Minerals, Nomenclature and Classification. A review of the compositions of 68 axinites containing over 10 wt% MnO reveals continuous solid solution between end member tinzenite and end member axinite-(Mn). Distinguishing tinzenite from axinite-(Mn) requires an analysis, either wet chemical or electron microprobe accompanied with an estimate of Fe (super 2+) /Fe (super 3+) ratio and assuming stoichiometric H and B. The distinction should be based exclusively on Ca content with the cutoff being Ca = 3atoms per formula unit (apfu). Compositions closely approaching end member tinzenite, have been found at Klucov near Trebic, Czech Republic and Jurvielle, Hautes-Pyrenees, France. The presence of tinzenite has been confirmed at 10 localities worldwide, at 9 of which tinzenite is found with quartz, rhodonite, Mn-bearing calcite or rhodochrosite in veinlets cutting stratiform manganese deposits or metachert. The tenth locality (Klucov) is entirely different: a pegmatite of the niobium-yttrium-fluorine family, where tinzenite occurs with quartz, K-feldspar and cassiterite.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 30
Serial Issue: 1
Title: Tinzenite, a member of the axinite group with formula revised to Ca (sub 2) Mn (sub 4) (super 2+) Al (sub 4) [B (sub 2) Si (sub 8) O (sub 30) ](OH) (sub 2)
Author(s): Grew, Edward S.
Affiliation: University of Maine, School of Earth and Climate Sciences, Orono, ME, United States
Pages: 177-182
Published: 201802
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 57
Accession Number: 2018-059730
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
N49°10'00" - N49°10'00", E15°55'60" - E15°55'60"
N42°49'00" - N42°49'00", E00°28'60" - E00°28'60"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2018
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