Kahlenbergite KAl<sub>11</sub>O<sub>17</sub>, a new <i>β</i>-alumina mineral and Fe-rich hibonite from the Hatrurim Basin, the Negev desert, Israel
<p>Kahlenbergite, ideally KAl<span class="inline-formula"><sub>11</sub></span>O<span class="inline-formula"><sub>17</sub></span>, and Fe-rich hibonite, CaAl<span class="inline-formula"><sub>10</sub>...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-07-01
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| Series: | European Journal of Mineralogy |
| Online Access: | https://ejm.copernicus.org/articles/33/341/2021/ejm-33-341-2021.pdf |
| Summary: | <p>Kahlenbergite, ideally KAl<span class="inline-formula"><sub>11</sub></span>O<span class="inline-formula"><sub>17</sub></span>, and Fe-rich
hibonite, CaAl<span class="inline-formula"><sub>10</sub></span>Fe<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>19</sub></span>, are high-temperature minerals found
in “olive” subunits of pyrometamorphic rocks, in the Hatrurim
Basin, the Negev desert, Israel. The crystal structures of both minerals are
refined using synchrotron radiation single-crystal diffraction data. The
structure of kahlenbergite (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>P</mi><msub><mn mathvariant="normal">6</mn><mn mathvariant="normal">3</mn></msub><mo>/</mo><mi>m</mi><mi>m</mi><mi>c</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="53pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="7b1b9eb9e06683e3971762901914ae6a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-33-341-2021-ie00001.svg" width="53pt" height="14pt" src="ejm-33-341-2021-ie00001.png"/></svg:svg></span></span>; <span class="inline-formula"><i>a</i>=5.6486(1)</span> Å; <span class="inline-formula"><i>b</i>=22.8970(3)</span> Å; <span class="inline-formula"><i>Z</i>=2</span>) exhibits triple spinel blocks and so-called R blocks. The spinel
blocks show mixed layers with AlO<span class="inline-formula"><sub>6</sub></span> octahedra and
(Al<span class="inline-formula"><sub>0.56</sub></span>Fe<span class="inline-formula"><sub>0.44</sub>)</span>O<span class="inline-formula"><sub>4</sub></span> tetrahedra and kagome layers with
(Al<span class="inline-formula"><sub>0.92</sub></span>Fe<span class="inline-formula"><sub>0.08</sub>)</span>O<span class="inline-formula"><sub>6</sub></span> octahedra. One-dimensional diffuse
scattering observed parallel to <span class="inline-formula"><i>c</i><sup>*</sup></span> implies stacking faults in the structure.
Also, in one of the investigated kahlenbergite crystals additional
reflections can be identified, which obviously belong to a second phase with
a smaller lattice parameter <span class="inline-formula"><i>c</i></span>: Fe<span class="inline-formula"><sup>3+</sup></span>-rich hibonite. The structure of
hibonite contains the same spinel blocks as kahlenbergite. The R blocks in
hibonite contain Ca atoms, AlO<span class="inline-formula"><sub>5</sub></span> bipyramids, and AlO<span class="inline-formula"><sub>6</sub></span> octahedra,
whereas the R blocks in kahlenbergite contain potassium atoms and AlO<span class="inline-formula"><sub>4</sub></span>
tetrahedra.</p> |
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| ISSN: | 0935-1221 1617-4011 |