Bobtraillite from Gejiu hyperagpaitic nepheline syenite, southwestern China: new occurrence and crystal structure
<p>A second occurrence of bobtraillite is described from the Gejiu nepheline syenite, southwestern China. The extremely rare and complex boron-bearing zirconium silicate is associated with albite, orthoclase, jadeite, fluorite, andradite, titanite, as well as other REE and zirconium-bearing mi...
| Main Authors: | , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-01-01
|
| Series: | European Journal of Mineralogy |
| Online Access: | https://ejm.copernicus.org/articles/35/65/2023/ejm-35-65-2023.pdf |
| Summary: | <p>A second occurrence of bobtraillite is described from the
Gejiu nepheline syenite, southwestern China. The extremely rare and complex
boron-bearing zirconium silicate is associated with albite, orthoclase,
jadeite, fluorite, andradite, titanite, as well as other REE and
zirconium-bearing minerals, catapleiite, moxuanxueite, låvenite,
eudialyte, britholite-(Ce), and calcioancylite-(La). The EMP and LA-ICP-MS
analyses of the studied material give an empirical formula:
(Na<span class="inline-formula"><sub>9.70</sub></span>Li<span class="inline-formula"><sub>0.42</sub></span>K<span class="inline-formula"><sub>0.08</sub>□<sub>1.80</sub></span>)<span class="inline-formula"><sub>Σ12.00</sub></span>(Sr<span class="inline-formula"><sub>10.61</sub></span>Ca<span class="inline-formula"><sub>1.14</sub></span>Fe<span class="inline-formula"><sub>0.07</sub>□<sub>0.18</sub></span>)<span class="inline-formula"><sub>Σ12.00</sub></span>(Zr<span class="inline-formula"><sub>12.87</sub></span>Ti<span class="inline-formula"><sub>0.53</sub></span>Nb<span class="inline-formula"><sub>0.31</sub></span>REE<span class="inline-formula"><sub>0.08</sub></span>Y<span class="inline-formula"><sub>0.06</sub></span>U<span class="inline-formula"><sub>0.02</sub></span>Th<span class="inline-formula"><sub>0.01</sub>□<sub>0.12</sub></span>)<span class="inline-formula"><sub>Σ14.00</sub></span>(Si<span class="inline-formula"><sub>42.41</sub></span>B<span class="inline-formula"><sub>5.59</sub></span>Al<span class="inline-formula"><sub>0.02</sub></span>)<span class="inline-formula"><sub>Σ48.02</sub></span>O<span class="inline-formula"><sub>132</sub></span>(OH)<span class="inline-formula"><sub>12</sub></span> <span class="inline-formula"><span class="Radical">⚫</span></span> 12H<span class="inline-formula"><sub>2</sub></span>O. Bobtraillite is trigonal,
with space group <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M25" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>P</mi><mover accent="true"><mn mathvariant="normal">3</mn><mo mathvariant="normal">¯</mo></mover><mi>c</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="3c1302eaea2aa69cf43c4367df4d285f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-65-2023-ie00001.svg" width="23pt" height="12pt" src="ejm-35-65-2023-ie00001.png"/></svg:svg></span></span>1, <span class="inline-formula"><i>a</i>=19.6977(6)</span>, <span class="inline-formula"><i>c</i>=9.9770(3)</span> Å, <span class="inline-formula"><i>V</i>=3352.4(2)</span> Å<span class="inline-formula"><sup>3</sup></span>, <span class="inline-formula"><i>Z</i>=1</span>. Single-crystal structure refinement revealed
that all sodium occupies the Na(1) and Na(2) sites; the site occupancy of
these two positions is 0.835(18) and 0.15(2), respectively, suggesting that
Na(1) site is Na dominant, while Na(2) is a vacancy-dominant site. The
[8]-coordinated site has been assigned to Sr and Ca, with free
occupancy factors, 0.874(10) and 0.126(10), respectively. These new data
indicate that the ideal formula of bobtraillite could be written as
(Na,<span class="inline-formula">□</span>)<span class="inline-formula"><sub>12</sub></span>(<span class="inline-formula">□</span>,Na)<span class="inline-formula"><sub>12</sub></span>Sr<span class="inline-formula"><sub>12</sub></span>Zr<span class="inline-formula"><sub>14</sub></span>(Si<span class="inline-formula"><sub>3</sub></span>O<span class="inline-formula"><sub>9</sub></span>)<span class="inline-formula"><sub>10</sub></span>[Si<span class="inline-formula"><sub>2</sub></span>BO<span class="inline-formula"><sub>7</sub></span>(OH)<span class="inline-formula"><sub>2</sub></span>]<span class="inline-formula"><sub>6</sub></span> <span class="inline-formula"><span class="Radical">⚫</span></span> 12H<span class="inline-formula"><sub>2</sub></span>O.</p> |
|---|---|
| ISSN: | 0935-1221 1617-4011 |