Manganrockbridgeite, Mn<sup>2+</sup><sub>2</sub>Fe<sup>3+</sup><sub>3</sub>(PO<sub>4</sub>)<sub>3</sub>(OH)<sub>4</sub>(H<sub>2</sub>O), a new member of the rockbridgeite group, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria
<p>Manganrockbridgeite, Mn<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant=&...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-04-01
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| Series: | European Journal of Mineralogy |
| Online Access: | https://ejm.copernicus.org/articles/35/295/2023/ejm-35-295-2023.pdf |
| Summary: | <p>Manganrockbridgeite,
Mn<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</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="12pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="f847710bcb164466748dff710f279cd8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00005.svg" width="12pt" height="16pt" src="ejm-35-295-2023-ie00005.png"/></svg:svg></span></span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</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="12pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="9149f9bd858bfe4181c78f6fa2338b56"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00006.svg" width="12pt" height="17pt" src="ejm-35-295-2023-ie00006.png"/></svg:svg></span></span>(PO<span class="inline-formula"><sub>4</sub></span>)<span class="inline-formula"><sub>3</sub></span>(OH)<span class="inline-formula"><sub>4</sub></span>(H<span class="inline-formula"><sub>2</sub></span>O), is a new
member of the rockbridgeite group, from the Hagendorf-Süd pegmatite,
Oberpfalz, Bavaria. It occurs in association with frondelite, kenngottite,
hureaulite and hematite. It forms compact intergrowths and clusters of shiny
greenish black blades up to 200 <span class="inline-formula">µ</span>m long and 20 <span class="inline-formula">µ</span>m wide but only a few micrometres thick. The crystals are elongated on [100] and flattened on
{001}, with perfect cleavage parallel to
{001}. Individual thin blades are green in
transmitted light and red under crossed polars. The calculated density is
3.40 g cm<span class="inline-formula"><sup>−3</sup></span>. Manganrockbridgeite is biaxial (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>+</mo><mo>/</mo><mo>-</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="9c7c30766d6581c7ab14ef35929c92be"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00007.svg" width="25pt" height="14pt" src="ejm-35-295-2023-ie00007.png"/></svg:svg></span></span>), with
<span class="inline-formula"><i>α</i>=</span> 1.795(5), <span class="inline-formula"><i>β</i>=</span> 1.805(calc), <span class="inline-formula"><i>γ</i>=1.815</span>(5)
(white light) and 2<span class="inline-formula"><i>V</i></span>(meas.) <span class="inline-formula">=</span> 90(2)<span class="inline-formula"><sup>∘</sup></span>. The empirical formula from
electron microprobe analyses, Mössbauer spectroscopy and crystal
structure refinement is
(Mn<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">1.07</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="f8d0c890d17a4fe5641fa830c8d9b888"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00008.svg" width="18pt" height="17pt" src="ejm-35-295-2023-ie00008.png"/></svg:svg></span></span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M24" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.69</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="6140eeb81283a299aad01dc1aa2300ba"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00009.svg" width="18pt" height="17pt" src="ejm-35-295-2023-ie00009.png"/></svg:svg></span></span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M25" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.16</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="4e168c2332dc045dff9c24f64490549b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00010.svg" width="18pt" height="17pt" src="ejm-35-295-2023-ie00010.png"/></svg:svg></span></span>)<span class="inline-formula"><sub>Σ1.92</sub></span>(Fe<span class="inline-formula"><sup>3+</sup></span>)<span class="inline-formula"><sub>2.88</sub></span>(PO<span class="inline-formula"><sub>4</sub></span>)<span class="inline-formula"><sub>3</sub></span>(OH)<span class="inline-formula"><sub>3.64</sub></span>(H<span class="inline-formula"><sub>2</sub></span>O)<span class="inline-formula"><sub>1.44</sub></span>.
Manganrockbridgeite has monoclinic symmetry with space group P2<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M34" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi/><mn mathvariant="normal">1</mn></msub><mo>/</mo><mi>m</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="25ef404f022c9fc67f6659919cdd7699"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00011.svg" width="23pt" height="14pt" src="ejm-35-295-2023-ie00011.png"/></svg:svg></span></span> and
unit-cell parameters <span class="inline-formula"><i>a</i>=5.198</span>(2), <span class="inline-formula"><i>b</i>=16.944</span>(5), <span class="inline-formula"><i>c</i>=7.451</span>(3) Å,
<span class="inline-formula"><i>β</i>=110.170</span>(9)<span class="inline-formula"><sup>∘</sup></span>, <span class="inline-formula"><i>V</i>=616.0</span>(4) Å<span class="inline-formula"><sup>3</sup></span> and <span class="inline-formula"><i>Z</i>=2</span>.
The crystal structure was refined using both laboratory and synchrotron
single-crystal diffraction data. Whereas other rockbridgeite-group minerals
have orthorhombic symmetry with a statistical distribution of
50 % Fe<span class="inline-formula"><sup>3+</sup></span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M44" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="9e2acdc284f0ee371079cabe514804d7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-295-2023-ie00012.svg" width="8pt" height="14pt" src="ejm-35-295-2023-ie00012.png"/></svg:svg></span></span> 50 % vacancies in <span class="inline-formula"><i>M</i></span>3-site octahedra forming face-shared
chains along the 5.2 Å axis, monoclinic manganrockbridgeite has full
ordering of Fe<span class="inline-formula"><sup>3+</sup></span> and vacancies in alternate <span class="inline-formula"><i>M</i></span>3 sites along the 5.2 Å
axis.</p> |
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| ISSN: | 0935-1221 1617-4011 |