Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)

Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)

<p>The new mineral dacostaite, K(Mg<span class="inline-formula"><sub>2</sub></span>Al)[Mg(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>6</sub></span>]&l...

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Main Authors: C. Biagioni, D. Mauro, J. Sejkora, Z. Dolníček, A. Dini, R. Škoda
Format: Article
Language:English
Published: Copernicus Publications 2025-01-01
Series:European Journal of Mineralogy
Online Access:https://ejm.copernicus.org/articles/37/39/2025/ejm-37-39-2025.pdf
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author C. Biagioni
C. Biagioni
D. Mauro
D. Mauro
J. Sejkora
Z. Dolníček
A. Dini
R. Škoda
author_facet C. Biagioni
C. Biagioni
D. Mauro
D. Mauro
J. Sejkora
Z. Dolníček
A. Dini
R. Škoda
author_sort C. Biagioni
collection DOAJ
description <p>The new mineral dacostaite, K(Mg<span class="inline-formula"><sub>2</sub></span>Al)[Mg(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>6</sub></span>]<span class="inline-formula"><sub>2</sub></span>(AsO<span class="inline-formula"><sub>4</sub></span>)<span class="inline-formula"><sub>2</sub></span>F<span class="inline-formula"><sub>6</sub></span> <span class="inline-formula">⋅</span> 2H<span class="inline-formula"><sub>2</sub></span>O, has been discovered in the Cetine di Cotorniano Mine, Chiusdino, Siena, Tuscany, Italy. It occurs as thin, colourless-to-white pseudo-hexagonal micaceous crystals up to 0.5 mm in size. The streak is white, and the lustre is silky. The cleavage is perfect on <span class="inline-formula"><i>{</i>001<i>}</i></span>. The empirical formula of dacostaite, based on (As <span class="inline-formula">+</span> P) <span class="inline-formula">=</span> 2 atoms per formula unit, is (K<span class="inline-formula"><sub>0.56</sub></span>Ca<span class="inline-formula"><sub>0.04</sub></span>Na<span class="inline-formula"><sub>0.03</sub>□<sub>0.37</sub></span>)<span class="inline-formula"><sub>Σ1.00</sub></span> (Al<span class="inline-formula"><sub>1.54</sub></span>Mg<span class="inline-formula"><sub>1.38</sub></span>Cu<span class="inline-formula"><sub>0.03</sub></span>Zn<span class="inline-formula"><sub>0.03</sub></span>)<span class="inline-formula"><sub>Σ2.98</sub></span> [Mg(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>6</sub></span>]<span class="inline-formula"><sub>2</sub></span> [(As<span class="inline-formula"><sub>0.99</sub></span>P<span class="inline-formula"><sub>0.01</sub>)</span>O<span class="inline-formula"><sub>4</sub></span>]<span class="inline-formula"><sub>2</sub></span> [F<span class="inline-formula"><sub>4.46</sub></span>(OH)<span class="inline-formula"><sub>1.46</sub></span>O<span class="inline-formula"><sub>0.08</sub></span>]<span class="inline-formula"><sub>Σ6.00</sub></span> <span class="inline-formula">⋅</span> 2H<span class="inline-formula"><sub>2</sub></span>O (<span class="inline-formula"><i>Z</i>=2</span>). Dacostaite is monoclinic, with a space group of <span class="inline-formula"><i>C</i></span>2/<span class="inline-formula"><i>m</i></span> and <span class="inline-formula"><i>a</i>=12.474(5)</span>, <span class="inline-formula"><i>b</i>=7.198(3)</span>, <span class="inline-formula"><i>c</i>=13.724(6)</span> Å, <span class="inline-formula"><i>β</i>=99.518(13)</span>°, and <span class="inline-formula"><i>V</i>=1215.3(8)</span> Å<span class="inline-formula"><sup>3</sup></span>. The crystal structure was solved using single-crystal X-ray diffraction data and refined to <span class="inline-formula"><i>R</i><sub>1</sub>=0.0927</span> for 1022 unique reflections with <span class="inline-formula"><i>F</i><sub><i>o</i></sub></span> <span class="inline-formula">&gt;</span> 4<span class="inline-formula"><i>σ</i></span> (<span class="inline-formula"><i>F</i><sub><i>o</i></sub></span>). The crystal structure of dacostaite can be described as formed by heteropolyhedral <span class="inline-formula"><i>{</i>001<i>}</i></span> layers and isolated Mg(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>6</sub></span> groups connected by H bonds. In the type material, dacostaite is associated with quartz, sulfur, gypsum, and a pharmacosiderite-like mineral in a small cavity of silicified limestone. Its genesis is related to the activity of oxidized (Al,F)-rich fluids during the late-stage evolution of the Sb ore deposit formerly exploited at the Cetine di Cotorniano Mine.</p>
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publishDate 2025-01-01
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series European Journal of Mineralogy
spelling doaj-art-cdf2a25cc1d04e9293422ee191e82b182025-01-20T10:20:35ZengCopernicus PublicationsEuropean Journal of Mineralogy0935-12211617-40112025-01-0137395210.5194/ejm-37-39-2025Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)C. Biagioni0C. Biagioni1D. Mauro2D. Mauro3J. Sejkora4Z. Dolníček5A. Dini6R. Škoda7Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, 56126 Pisa, ItalyCentro per l'Integrazione della Strumentazione scientifica dell'Università di Pisa (CISUP), Università di Pisa, Pisa, ItalyDipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, 56126 Pisa, ItalyMuseo di Storia Naturale, Università di Pisa, Via Roma 79, 56011 Calci, ItalyDepartment of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Prague, Czech RepublicDepartment of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Prague, Czech RepublicIstituto di Geoscienze e Georisorse, Consiglio Nazionale delle Ricerche, Via Moruzzi 1, 56124 Pisa, ItalyDepartment of Geological Sciences, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic<p>The new mineral dacostaite, K(Mg<span class="inline-formula"><sub>2</sub></span>Al)[Mg(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>6</sub></span>]<span class="inline-formula"><sub>2</sub></span>(AsO<span class="inline-formula"><sub>4</sub></span>)<span class="inline-formula"><sub>2</sub></span>F<span class="inline-formula"><sub>6</sub></span> <span class="inline-formula">⋅</span> 2H<span class="inline-formula"><sub>2</sub></span>O, has been discovered in the Cetine di Cotorniano Mine, Chiusdino, Siena, Tuscany, Italy. It occurs as thin, colourless-to-white pseudo-hexagonal micaceous crystals up to 0.5 mm in size. The streak is white, and the lustre is silky. The cleavage is perfect on <span class="inline-formula"><i>{</i>001<i>}</i></span>. The empirical formula of dacostaite, based on (As <span class="inline-formula">+</span> P) <span class="inline-formula">=</span> 2 atoms per formula unit, is (K<span class="inline-formula"><sub>0.56</sub></span>Ca<span class="inline-formula"><sub>0.04</sub></span>Na<span class="inline-formula"><sub>0.03</sub>□<sub>0.37</sub></span>)<span class="inline-formula"><sub>Σ1.00</sub></span> (Al<span class="inline-formula"><sub>1.54</sub></span>Mg<span class="inline-formula"><sub>1.38</sub></span>Cu<span class="inline-formula"><sub>0.03</sub></span>Zn<span class="inline-formula"><sub>0.03</sub></span>)<span class="inline-formula"><sub>Σ2.98</sub></span> [Mg(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>6</sub></span>]<span class="inline-formula"><sub>2</sub></span> [(As<span class="inline-formula"><sub>0.99</sub></span>P<span class="inline-formula"><sub>0.01</sub>)</span>O<span class="inline-formula"><sub>4</sub></span>]<span class="inline-formula"><sub>2</sub></span> [F<span class="inline-formula"><sub>4.46</sub></span>(OH)<span class="inline-formula"><sub>1.46</sub></span>O<span class="inline-formula"><sub>0.08</sub></span>]<span class="inline-formula"><sub>Σ6.00</sub></span> <span class="inline-formula">⋅</span> 2H<span class="inline-formula"><sub>2</sub></span>O (<span class="inline-formula"><i>Z</i>=2</span>). Dacostaite is monoclinic, with a space group of <span class="inline-formula"><i>C</i></span>2/<span class="inline-formula"><i>m</i></span> and <span class="inline-formula"><i>a</i>=12.474(5)</span>, <span class="inline-formula"><i>b</i>=7.198(3)</span>, <span class="inline-formula"><i>c</i>=13.724(6)</span> Å, <span class="inline-formula"><i>β</i>=99.518(13)</span>°, and <span class="inline-formula"><i>V</i>=1215.3(8)</span> Å<span class="inline-formula"><sup>3</sup></span>. The crystal structure was solved using single-crystal X-ray diffraction data and refined to <span class="inline-formula"><i>R</i><sub>1</sub>=0.0927</span> for 1022 unique reflections with <span class="inline-formula"><i>F</i><sub><i>o</i></sub></span> <span class="inline-formula">&gt;</span> 4<span class="inline-formula"><i>σ</i></span> (<span class="inline-formula"><i>F</i><sub><i>o</i></sub></span>). The crystal structure of dacostaite can be described as formed by heteropolyhedral <span class="inline-formula"><i>{</i>001<i>}</i></span> layers and isolated Mg(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>6</sub></span> groups connected by H bonds. In the type material, dacostaite is associated with quartz, sulfur, gypsum, and a pharmacosiderite-like mineral in a small cavity of silicified limestone. Its genesis is related to the activity of oxidized (Al,F)-rich fluids during the late-stage evolution of the Sb ore deposit formerly exploited at the Cetine di Cotorniano Mine.</p>https://ejm.copernicus.org/articles/37/39/2025/ejm-37-39-2025.pdf
spellingShingle C. Biagioni
C. Biagioni
D. Mauro
D. Mauro
J. Sejkora
Z. Dolníček
A. Dini
R. Škoda
Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)
European Journal of Mineralogy
title Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)
title_full Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)
title_fullStr Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)
title_full_unstemmed Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)
title_short Dacostaite, K(Mg<sub>2</sub>Al)[Mg(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>(AsO<sub>4</sub>)<sub>2</sub>F<sub>6</sub>&thinsp; ⋅ &thinsp;2H<sub>2</sub>O, a new fluoride–arsenate mineral from the Cetine di Cotorniano Mine (Tuscany, Italy)
title_sort dacostaite k mg sub 2 sub al mg h sub 2 sub o sub 6 sub sub 2 sub aso sub 4 sub sub 2 sub f sub 6 sub thinsp ⋅ thinsp 2h sub 2 sub o a new fluoride arsenate mineral from the cetine di cotorniano mine tuscany italy
url https://ejm.copernicus.org/articles/37/39/2025/ejm-37-39-2025.pdf
work_keys_str_mv AT cbiagioni dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly
AT cbiagioni dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly
AT dmauro dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly
AT dmauro dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly
AT jsejkora dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly
AT zdolnicek dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly
AT adini dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly
AT rskoda dacostaitekmgsub2subalmghsub2subosub6subsub2subasosub4subsub2subfsub6subthinspthinsp2hsub2suboanewfluoridearsenatemineralfromthecetinedicotornianominetuscanyitaly

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