Ellinaite, CaCr<sub>2</sub>O<sub>4</sub>, a new natural post-spinel oxide from Hatrurim Basin, Israel, and Juína kimberlite field, Brazil
<p>Ellinaite, a natural analog of the post-spinel phase <span class="inline-formula"><i>β</i></span>-CaCr<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub><...
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| Autores principales: | , , , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/802cc9c1293e48f7ab9e950effce8a05 |
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| Sumario: | <p>Ellinaite, a natural analog of the post-spinel phase
<span class="inline-formula"><i>β</i></span>-CaCr<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span>, was discovered at the Hatrurim Basin, Hatrurim
pyrometamorphic formation (the Mottled Zone), Israel, and in an inclusion
within the super-deep diamond collected at the placer of the Sorriso River,
Juína kimberlite field, Brazil. Ellinaite at the Hatrurim Basin is
confined to a reduced rankinite–gehlenite paralava, where it occurs as
subhedral grains up to 30 <span class="inline-formula">µ</span>m in association with gehlenite, rankinite
and pyrrhotite or forms the rims overgrowing zoned
chromite–magnesiochromite. The empirical formula of the Hatrurim sample is
(Ca<span class="inline-formula"><sub>0.960</sub></span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.016</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="22pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="715ab2c0c68c332c1914a69030b21427"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-33-727-2021-ie00001.svg" width="22pt" height="17pt" src="ejm-33-727-2021-ie00001.png"/></svg:svg></span></span>Na<span class="inline-formula"><sub>0.012</sub></span>Mg<span class="inline-formula"><sub>0.003</sub>)<sub>0.992</sub></span>(Cr<span class="inline-formula"><sub>1.731</sub></span>V<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.183</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="22pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="9e675a19d1978afe3aea17bc8867c91e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-33-727-2021-ie00002.svg" width="22pt" height="17pt" src="ejm-33-727-2021-ie00002.png"/></svg:svg></span></span>Ti<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.068</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="22pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="ab1761a8fdd0a4d4dad565b54ca3ba37"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-33-727-2021-ie00003.svg" width="22pt" height="17pt" src="ejm-33-727-2021-ie00003.png"/></svg:svg></span></span>Al<span class="inline-formula"><sub>0.023</sub></span>Ti<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.003</mn><mrow><mn mathvariant="normal">4</mn><mo>+</mo></mrow></msubsup><msub><mo>)</mo><mn mathvariant="normal">2.008</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="35234c0de1ff71fb1dedfc110ba65ed6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-33-727-2021-ie00004.svg" width="46pt" height="17pt" src="ejm-33-727-2021-ie00004.png"/></svg:svg></span></span>O<span class="inline-formula"><sub>4</sub></span>. The mineral
crystallizes in the orthorhombic system, space group <i>Pnma</i>, unit-cell parameters
refined from X-ray single-crystal data: <span class="inline-formula"><i>a</i></span> 8.868(9), <span class="inline-formula"><i>b</i></span> 2.885(3), <span class="inline-formula"><i>c</i></span> 10.355(11) Å, <span class="inline-formula"><i>V</i></span> 264.9(5) Å<span class="inline-formula"><sup>3</sup></span> and <span class="inline-formula"><i>Z</i>=4</span>. The crystal structure of ellinaite
from the Hatrurim Basin has been solved and refined to <span class="inline-formula"><i>R</i><sub>1</sub>=0.0588</span>
based on 388 independent observed reflections. Ellinaite in the Juína
diamond occurs within the micron-sized polyphase inclusion in association
with ferropericlase, magnesioferrite, orthorhombic MgCr<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span>,
unidentified iron carbide and graphite. Its empirical formula is
Ca<span class="inline-formula"><sub>1.07</sub></span>(Cr<span class="inline-formula"><sub>1.71</sub></span>Fe<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M30" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">0.06</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="5e2b230bd4d17aba654069a1b5c33c5e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-33-727-2021-ie00005.svg" width="18pt" height="17pt" src="ejm-33-727-2021-ie00005.png"/></svg:svg></span></span>V<span class="inline-formula"><sub>0.06</sub></span>Ti<span class="inline-formula"><sub>0.03</sub></span>Al<span class="inline-formula"><sub>0.03</sub></span>Mg<span class="inline-formula"><sub>0.02</sub></span>Mn<span class="inline-formula"><sub>0.02</sub>)<sub>Σ1.93</sub></span>O<span class="inline-formula"><sub>4</sub></span>. The unit-cell parameters obtained from HRTEM data are as follows: space
group <i>Pnma</i>, <span class="inline-formula"><i>a</i></span> 9.017, <span class="inline-formula"><i>b</i></span> 2.874 Å, <span class="inline-formula"><i>c</i></span> 10.170 Å, <span class="inline-formula"><i>V</i></span> 263.55 Å<span class="inline-formula"><sup>3</sup></span>, <span class="inline-formula"><i>Z</i>=4</span>.
Ellinaite belongs to a group of natural tunnel-structured oxides of the
general formula AB<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span>, the so-called post-spinel minerals: marokite
CaMn<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span>, xieite FeCr<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span>, harmunite CaFe<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span>,
wernerkrauseite CaFe<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">2</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="43bc178c8c5b168fa3edb61f0d79ee3f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-33-727-2021-ie00006.svg" width="12pt" height="17pt" src="ejm-33-727-2021-ie00006.png"/></svg:svg></span></span>Mn<span class="inline-formula"><sup>4+</sup></span>O<span class="inline-formula"><sub>6</sub></span>, chenmingite
FeCr<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span>, maohokite MgFe<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>4</sub></span> and tschaunerite
Fe(FeTi)O<span class="inline-formula"><sub>4</sub></span>. The mineral from both occurrences seems to be crystallized
under highly reduced conditions at high temperatures (<span class="inline-formula"><i>></i>1000</span> <span class="inline-formula"><sup>∘</sup></span>C), but under different pressure: near-surface (Hatrurim Basin)
and lower mantle (Juína diamond).</p> |
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