Macraeite, [(H₂O)K]Mn₂(Fe₂Ti)(PO₄)₄[O(OH)](H₂O)₁₀  ⋅  4H₂O, a new monoclinic paulkerrite-group mineral, from the Cubos–Mesquitela–Mangualde pegmatite, Portugal

<p>Macraeite, [(H<span class="inline-formula">₂</span>O)K]Mn<span class="inline-formula">₂</span>(Fe<span class="inline-formula">₂</span>Ti)(PO<span class="inline-formula">₄</span>)<span class="inline-formula">₄</span>[O(OH)](H<span class="inline-formula">₂</span>O)<span class="inline-formula">₁₀</span> <span class="inline-formula">⋅</span> 4H<span class="inline-formula">₂</span>O, is a new monoclinic member of the paulkerrite group, from the Cubos–Mesquitela–Mangualde pegmatite, Mangualde, Portugal. It was found in phosphate nodules of weathered triplite, heterosite, and lithiophilite. Associated minerals are strengite, triplite, bermanite, phosphosiderite, and switzerite.</p> <p>Macraeite forms colourless to light-greenish-yellow pseudo-rhombic dodecahedral-shaped crystals up to 0.15 mm. The crystals are equant with forms {010}, {001}, {111}, and {<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mover accent="true"><mn mathvariant="normal">1</mn><mo mathvariant="normal">‾</mo></mover></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="52ccb44bd52443b5c78783e0d1501948"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-36-267-2024-ie00001.svg" width="8pt" height="13pt" src="ejm-36-267-2024-ie00001.png"/></svg:svg></span></span>11}. The calculated density is 2.39 g cm<span class="inline-formula">⁻³</span>. Optically, macraeite crystals are biaxial (<span class="inline-formula">+</span>), with <span class="inline-formula"><i>α</i>=1.605(3)</span>, <span class="inline-formula"><i>β</i>=1.611(3)</span>, <span class="inline-formula"><i>γ</i>=1.646(3)</span> (measured in white light), and 2<span class="inline-formula"><i>V</i></span>(meas) <span class="inline-formula">=</span> 45(3)°. The empirical formula from electron microprobe analyses and structure refinement is <span class="inline-formula">^<i>A</i>1</span>[(H<span class="inline-formula">₂</span>O)<span class="inline-formula">_0.83</span>K<span class="inline-formula">_0.17</span>]<span class="inline-formula">_Σ1.00</span> <span class="inline-formula">^<i>A</i>2</span>[K<span class="inline-formula">_0.65</span>(H<span class="inline-formula">₂</span>O)<span class="inline-formula">_0.35</span>]<span class="inline-formula">_Σ1.00</span> <span class="inline-formula">^<i>M</i>1</span>(Mn<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M38" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mrow><mn mathvariant="normal">1.98</mn><mspace width="0.125em" linebreak="nobreak"/><mo>□</mo><mspace width="0.125em" linebreak="nobreak"/><mn mathvariant="normal">0.02</mn></mrow><mrow><mn mathvariant="normal">2</mn><mo>+</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="42pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="99e8122d4196e0edb14c3852ff48beb8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-36-267-2024-ie00002.svg" width="42pt" height="17pt" src="ejm-36-267-2024-ie00002.png"/></svg:svg></span></span>)<span class="inline-formula">_Σ2.00</span> <span class="inline-formula">^<i>M</i>2</span>(Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M41" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">1.09</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="ff7025d9a180851be09b0a5a9dafe4b6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-36-267-2024-ie00003.svg" width="18pt" height="17pt" src="ejm-36-267-2024-ie00003.png"/></svg:svg></span></span>Al<span class="inline-formula">_0.31</span>Ti<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M43" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.52</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="a64a42ebdbe27224f4a9389f74808ed1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-36-267-2024-ie00004.svg" width="18pt" height="17pt" src="ejm-36-267-2024-ie00004.png"/></svg:svg></span></span>Mg<span class="inline-formula">_0.08</span>)<span class="inline-formula">_Σ2.00</span> <span class="inline-formula">^<i>M</i>3</span>(Ti<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">0.66</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="94c65da2b790470e2ec843d87f83884b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-36-267-2024-ie00005.svg" width="18pt" height="17pt" src="ejm-36-267-2024-ie00005.png"/></svg:svg></span></span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M48" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.34</mn><mrow><mn mathvariant="normal">3</mn><mo>+</mo></mrow></msubsup><msub><mo>)</mo><mrow><mi mathvariant="normal">Σ</mi><mn mathvariant="normal">1.00</mn></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="42pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="e052b7d79f69e15a421fec742b5c78b6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-36-267-2024-ie00006.svg" width="42pt" height="17pt" src="ejm-36-267-2024-ie00006.png"/></svg:svg></span></span> (PO<span class="inline-formula">₄</span>)<span class="inline-formula">₄</span> <span class="inline-formula">^<i>X</i></span>[O<span class="inline-formula">_0.87</span>F<span class="inline-formula">_0.53</span>(OH)<span class="inline-formula">_0.60</span>]<span class="inline-formula">_Σ2.00</span>(H<span class="inline-formula">₂</span>O)<span class="inline-formula">₁₀</span> <span class="inline-formula">⋅</span> 4H<span class="inline-formula">₂</span>O.</p> <p>Macraeite has monoclinic symmetry with space group <span class="inline-formula"><i>P</i></span>2<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M61" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi/><mn mathvariant="normal">1</mn></msub><mo>/</mo><mi>c</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="20pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="18efce390d1a45e2eec99053bb843bb0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-36-267-2024-ie00007.svg" width="20pt" height="14pt" src="ejm-36-267-2024-ie00007.png"/></svg:svg></span></span> and unit-cell parameters <span class="inline-formula"><i>a</i>=10.562(2)</span> Å, <span class="inline-formula"><i>b</i>=20.725(4)</span> Å, <span class="inline-formula"><i>c</i>=12.416(2)</span> Å, <span class="inline-formula"><i>β</i>=90.09(3)</span>°, <span class="inline-formula"><i>V</i>=2717.8(9)</span> Å<span class="inline-formula">³</span>, and <span class="inline-formula"><i>Z</i>=4</span>. The crystal structure was refined using synchrotron single-crystal data to <i>wR</i><span class="inline-formula">_obs=0.065</span> for 4990 reflections with <span class="inline-formula"><i>I</i><i>&gt;</i>3<i>σ</i>(<i>I</i>)</span>. Macraeite is isostructural with the paulkerrite-group minerals rewitzerite and paulkerrite, with ordering of K and H<span class="inline-formula">₂</span>O at different <span class="inline-formula"><i>A</i></span> sites (<span class="inline-formula"><i>A</i></span>1 and <span class="inline-formula"><i>A</i></span>2) of the general formula <span class="inline-formula"><i>A</i></span>1<span class="inline-formula"><i>A</i></span>2<span class="inline-formula"><i>M</i></span>1<span class="inline-formula">₂<i>M</i></span>2<span class="inline-formula">₂<i>M</i></span>3(PO<span class="inline-formula">₄</span>)<span class="inline-formula">₄<i>X</i>₂</span>(H<span class="inline-formula">₂</span>O)<span class="inline-formula">₁₀</span> <span class="inline-formula">⋅</span> 4H<span class="inline-formula">₂</span>O, whereas in the orthorhombic member, benyacarite, K and H<span class="inline-formula">₂</span>O are disordered at a single <span class="inline-formula"><i>A</i></span> site.</p>