Revised formula of tinzenite

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Marco E. Ciriotti
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Revised formula of tinzenite

Messaggio da Marco E. Ciriotti » dom 25 feb, 2018 12:46

Prossima pubblicazione.

Referenza:
▪ Grew, E.S. (2018): Tinzenite, a member of the axinite group with formula revised to Ca2Mn2+4Al4[B2Si8O30](OH)2. European Journal of Mineralogy, 30, (in press).

Abstract:
The official International Mineralogical Association (IMA) list of minerals had given the formula for the tinzenite, an axinite-group mineral, as Ca6Al4[B2Si8O30](OH)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 Mn2+ than the Mn end-member, axinite-(Mn), Ca4Mn2Al4[B2Si8O30](OH)2. Revision of the tinzenite formula to Ca2Mn2+4Al4[B2Si8O30](OH)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 Fe2+/Fe3+ 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 Klučov near Třebíč, Czech Republic and Jurvielle, Hautes-Pyrénées, France. The presence of tinzenite has been confirmed at ten localities worldwide, at nine of which tinzenite is found with quartz, rhodonite, Mn-bearing calcite or rhodochrosite in veinlets cutting stratiform manganese deposits or metachert. The tenth locality (Klučov) is entirely different: a pegmatite of the niobium-yttrium-fluorine family, where tinzenite occurs with quartz, K-feldspar and cassiterite.
Marco E. Ciriotti

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Marco E. Ciriotti
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Re: Revised formula of tinzenite

Messaggio da Marco E. Ciriotti » mer 28 feb, 2018 13:32

Probabilmente non sarebbe male ricontrollare le occorrenze italiane...
Marco E. Ciriotti

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Marco E. Ciriotti
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Re: Revised formula of tinzenite

Messaggio da Marco E. Ciriotti » gio 03 mag, 2018 17:44

Pubblicazione effettuata.

Referenza:
▪ Grew, E.S. (2018): Tinzenite, a member of the axinite group with formula revised to Ca2Mn2+4Al4[B2Si8O30](OH)2. European Journal of Mineralogy, 30, 177-182.

Abstract:
The official International Mineralogical Association (IMA) list of minerals had given the formula for the tinzenite, an axinite-group mineral, as Ca6Al4[B2Si8O30](OH)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 Mn2+ than the Mn end-member, axinite-(Mn), Ca4Mn2Al4[B2Si8O30](OH)2. Revision of the tinzenite formula to Ca2Mn2+4Al4[B2Si8O30](OH)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 Fe2+/Fe3+ 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 Klučov near Třebíč, Czech Republic and Jurvielle, Hautes-Pyrénées, France. The presence of tinzenite has been confirmed at ten localities worldwide, at nine of which tinzenite is found with quartz, rhodonite, Mn-bearing calcite or rhodochrosite in veinlets cutting stratiform manganese deposits or metachert. The tenth locality (Klučov) is entirely different: a pegmatite of the niobium-yttrium-fluorine family, where tinzenite occurs with quartz, K-feldspar and cassiterite.

NdR: la seguente formula è più esplicativa di quella proposta e in linea con le altre specie del gruppo dell'axinite: [Ca2Mn2+4Al4](BO)2(Si2O7)4(OH)2. Meglio ancora [Ca2Mn2+2Mn2+2Al4](BO)2(Si2O7)4(OH)2.
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Roberto Bracco
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Re: Revised formula of tinzenite

Messaggio da Roberto Bracco » sab 05 mag, 2018 19:55

Marco E. Ciriotti ha scritto:
mer 28 feb, 2018 13:32
Probabilmente non sarebbe male ricontrollare le occorrenze italiane...
A suo tempo avevamo spedito una campionatura di "axiniti" liguri ad Andreozzi a Roma... chissà che ne è stato...
Roberto Bracco - AMI Liguria

Perché seguire il calcio, quando accanto c'è lo scandio e poco più in là il vanadio?

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Marco E. Ciriotti
Messaggi: 24906
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Re: Revised formula of tinzenite

Messaggio da Marco E. Ciriotti » sab 05 mag, 2018 20:21

A suo tempo avevamo spedito una campionatura di "axiniti" liguri ad Andreozzi a Roma... chissà che ne è stato...
Gianni Andreozzi, proprio oggi, mi ha passato l'abstract che presenterà a Catania, relativo ai lavori effettuati sui campioni della Val Graveglia.
Marco E. Ciriotti

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Marco E. Ciriotti
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Re: Revised formula of tinzenite

Messaggio da Marco E. Ciriotti » gio 24 mag, 2018 21:02

Roberto, in funzione del messaggio precedente, ti passerò privatamente, non appena definito, l'abstract in questione.
Marco E. Ciriotti

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Roberto Bracco
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Re: Revised formula of tinzenite

Messaggio da Roberto Bracco » sab 26 mag, 2018 10:27

Molto bene, grazie! Tutta manna per la mineralogia ligure sempre in cerca di impunture sistematiche...
Roberto Bracco - AMI Liguria

Perché seguire il calcio, quando accanto c'è lo scandio e poco più in là il vanadio?

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Marco E. Ciriotti
Messaggi: 24906
Iscritto il: ven 25 giu, 2004 11:31
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Re: Revised formula of tinzenite

Messaggio da Marco E. Ciriotti » sab 26 mag, 2018 11:12

Spedito. Seguirà, a breve, un regolare articolo.
Marco E. Ciriotti

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