Pleysteinite, [(H₂O)_0.5K_0.5]₂Mn₂Al₃(PO₄)₄F₂(H₂O)₁₀  ⋅  4H₂O, the Al analogue of benyacarite, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany

• Published in: European Journal of Mineralogy
• Main Authors: I. E. Grey, R. Hochleitner, C. Rewitzer, A. R. Kampf, C. M. MacRae, R. W. Gable, W. G. Mumme, E. Keck, C. Davidson
• Format: Article
• Language: English
• Published: Copernicus Publications 2023-03-01
• Online Access: https://ejm.copernicus.org/articles/35/189/2023/ejm-35-189-2023.pdf
• ISSN: 0935-1221; 1617-4011

<p>Pleysteinite, [(H<span class="inline-formula">₂</span>O)<span class="inline-formula">_0.5</span>K<span class="inline-formula">_0.5</span>]<span class="inline-formula">₂</span>Mn<span class="inline-formula">₂</span>Al<span class="inline-formula">₃</span>(PO<span class="inline-formula">₄</span>)<span class="inline-formula">₄</span>F<span class="inline-formula">₂</span>(H<span class="inline-formula">₂</span>O)<span class="inline-formula">₁₀</span> <span class="inline-formula"><span class="Radical">⚫</span></span> 4H<span class="inline-formula">₂</span>O, is the aluminium analogue of benyacarite, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in specimens of altered zwieselite, in association with nordgauite, fluellite, rockbridgeite, pyrite and columbite. Pleysteinite occurs as isolated and small aggregates of colourless, stubby prisms that are typically 10 to 30 <span class="inline-formula">µ</span>m wide and up to 100 <span class="inline-formula">µ</span>m long. The crystals are flattened on <span class="inline-formula"><i>{</i>010<i>}</i></span> and bounded by <span class="inline-formula"><i>{</i>111<i>}</i></span>, <span class="inline-formula"><i>{</i>100<i>}</i></span> and <span class="inline-formula"><i>{</i>001<i>}</i></span> planes. The calculated density is 2.34 g cm<span class="inline-formula">⁻³</span>. Optically, pleysteinite crystals are biaxial (<span class="inline-formula">+</span>), with <span class="inline-formula"><i>α</i>=1.566(2)</span>, <span class="inline-formula"><i>β</i>=1.580(2)</span>, <span class="inline-formula"><i>γ</i>=1.600(2)</span> (measured in white light) and 2<span class="inline-formula"><i>V</i></span>(meas.) <span class="inline-formula">=</span> 80(1)<span class="inline-formula">^∘</span>. The empirical formula from electron microprobe analyses and structure refinement is [(H<span class="inline-formula">₂</span>O)<span class="inline-formula">_0.50</span>K<span class="inline-formula">_0.50</span>]<span class="inline-formula">₂</span>(Mn<span class="inline-formula">_1.20</span>Mg<span class="inline-formula">_0.49</span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M47" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.27</mn><mrow><mn mathvariant="normal">2</mn><mo>+</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="18pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="25ed154b484de21b298099844df14fd1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-189-2023-ie00001.svg" width="18pt" height="17pt" src="ejm-35-189-2023-ie00001.png"/></svg:svg></span></span>Zn<span class="inline-formula">_0.05</span>)<span class="inline-formula">_∑2.01</span>(Al<span class="inline-formula">_1.63</span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M51" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.20</mn><mrow><mn mathvariant="normal">3</mn><mo>+</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="18pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="8c0d36a3e1000b3810412acd425e8868"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-189-2023-ie00002.svg" width="18pt" height="17pt" src="ejm-35-189-2023-ie00002.png"/></svg:svg></span></span>Ti<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M52" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.19</mn><mrow><mn mathvariant="normal">4</mn><mo>+</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="18pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="db913f3976347a17e5c7d1230b79631b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-189-2023-ie00003.svg" width="18pt" height="17pt" src="ejm-35-189-2023-ie00003.png"/></svg:svg></span></span>)<span class="inline-formula">_∑2.02</span>(Al<span class="inline-formula">_0.56</span>Ti<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M55" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.44</mn><mrow><mn mathvariant="normal">4</mn><mo>+</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="18pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="8badef26f19f19d825d41c365752284d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-189-2023-ie00004.svg" width="18pt" height="17pt" src="ejm-35-189-2023-ie00004.png"/></svg:svg></span></span>) (PO<span class="inline-formula">₄</span>)<span class="inline-formula">_4.02</span>[F<span class="inline-formula">_0.58</span>O<span class="inline-formula">_0.31</span>(OH)<span class="inline-formula">_0.11</span>]<span class="inline-formula">₂</span>(H<span class="inline-formula">₂</span>O)<span class="inline-formula">₁₀</span> <span class="inline-formula"><span class="Radical">⚫</span></span> 3.92H<span class="inline-formula">₂</span>O. Pleysteinite has orthorhombic symmetry, with space group <i>Pbca</i> and unit-cell parameters <span class="inline-formula"><i>a</i></span> <span class="inline-formula">=</span> 10.4133(8) Å, <span class="inline-formula"><i>b</i>=20.5242(17)</span> Å, <span class="inline-formula"><i>c</i>=12.2651(13)</span> Å, <span class="inline-formula"><i>V</i>=2621.4(4)</span> Å<span class="inline-formula">³</span> and <span class="inline-formula"><i>Z</i>=4</span>. The crystal structure was refined using single-crystal data to <i>wR</i><span class="inline-formula">_obs=0.054</span> for 1692 reflections with <span class="inline-formula"><i>I</i>&gt;3<i>σ</i>(<i>I</i>)</span>. The crystal structure contains corner-connected linear trimers of Al-centred octahedra that share corners with PO<span class="inline-formula">₄</span> tetrahedra to form 10-member rings parallel to (010). K<span class="inline-formula">⁺</span> cations and water molecules are located in the rings. Additional corner-sharing of the PO<span class="inline-formula">₄</span> tetrahedra with Mn(H<span class="inline-formula">₂</span>O)<span class="inline-formula">₄</span>O<span class="inline-formula">₂</span> octahedra occurs along [010] to complete the 3D framework structure.</p>