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A highly hydrated variety of elpidite from the Khibiny alkaline complex, Kola Peninsula, Russia
An unusual highly hydrated and Na-depleted variety of elpidite was identified in a hydrothermally altered peralkaline pegmatite at Mt. Yukspor in the Khibiny alkaline complex, Kola Peninsula, Russia. It differs from ‘ordinary’ elpidite, ideally Na 2 ZrSi 6 O 15 ⋅3H 2 O, in its crystal chemical featu...
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| Published in: | Mineralogical magazine 2021-08, Vol.85 (4), p.627-633 |
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| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | English |
| Subjects: | |
| Citations: | Items that this one cites Items that cite this one |
| Online Access: | Get full text |
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| Summary: | An unusual highly hydrated and Na-depleted variety of elpidite was identified in a hydrothermally altered peralkaline pegmatite at Mt. Yukspor in the Khibiny alkaline complex, Kola Peninsula, Russia. It differs from ‘ordinary’ elpidite, ideally Na
2
ZrSi
6
O
15
⋅3H
2
O, in its crystal chemical features, infrared spectrum and optical characteristics. The chemical composition (wt.%, electron microprobe, H
2
O by TGA) is: Na
2
O 5.45, K
2
O 0.67, CaO 0.05, SiO
2
60.32, TiO
2
1.34, ZrO
2
18.43, Nb
2
O
5
0.65, H
2
O 12.80, total 99.71. The empirical formula calculated on the basis of 6 Si and 15 O atoms is [(Na
1.05
K
0.08
Ca
0.01
)
Σ1.14
(H
3
O)
0.74
]
Σ1.88
(Zr
0.89
Ti
0.10
Nb
0.03
)
Σ1.02
Si
6
O
15
⋅3.47H
2
O; the H
2
O:H
3
O ratio was calculated from the charge balance requirement, taking into account the results of crystal structure refinement. The highly hydrated variety of elpidite is orthorhombic,
Pma
2,
a
= 14.5916(6),
b
= 7.3294(3),
c
= 7.1387(2) Å,
V
= 763.47(5) Å
3
and
Z
= 2. The crystal structure was solved from single-crystal X-ray diffraction data,
R
1
= 3.43%. The structure is based upon an elpidite-type heteropolyhedral Zr–Si–O framework with Na
+
and H
3
O
+
cations and H
2
O molecules in the zeolitic channels. Hydronium cations substitute for water molecules in one of the extra-framework sites. This variety of elpidite could be considered as an intermediate product of natural ion-exchange reaction between ‘ordinary’ elpidite and a low-temperature hydrothermal fluid. |
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| ISSN: | 0026-461X 1471-8022 |
| DOI: | 10.1180/mgm.2020.96 |