Bafertisite
and jinshajiangite from the Gremyakha-Vyrmes alkaline complex,
Lykova I.S.*, Pekov
I.V.*,*, Kononkova N.N.**, Shpachenko A.K.***
*
**Vernadsky Institute of Geochemistry and Analytical Chemistry RAS,
***Geological
The layered titanosilicates bafertisite,
Ba2Fe4Ti2O2(Si2O7)2(OH)4,
Áand jinshajiangite, NaBaFe4Ti2O(Si2O7)2(OH)
Minerals of the bafertisite group were not reported from
Gremyakha-Vyrmes before. For jinshajiangite, it is first find in
The described minerals were found in a pegmatite
related to alkaline granites at northern coast of the Gremyakha lake. Jinshajiangite occurs
as needle-shaped crystals up to
Bafertisite and jinshajiangite have been identified by chemical, X-ray diffraction
and infrared spectroscopy data.
The X-ray powder patterns of bafertisite
and jinshajiangite from Gremyakha-Vyrmes are similar to ones of these minerals studied
earlier (Kuan Ya-Hsien et al.,
1963; Hong
Wenxing, Fu Pinqiu, 1982). The main basal reflection (002) of Kola
jinshajiangite is characterized by the interplanar spacing 10.40 Å, the 001
reflex of Kola bafertisite is 10.95 Å.
The chemical composition of bafertisite
and jinshajiangite was studied using the electron microprobe. Formulae were
calculated basing on 4(Si+Al). All iron was considered as bivalent, the O/OH
ratio was calculated by charge balance. The empirical formulae (cations have groupped
according to structural data for the minerals) are:
bafertisite:
(Ba1.98Na0.04K0.03)Σ1.05(Fe3.43Mn0.37Mg0.03)Σ3.83(Ti2.02Nb0.03)Σ2.05(Si3.92Al0.08O14)(O1.84OH0.16)Σ2.00(OH2.39F1.61)Σ4.00;
jinshajiangite:
(Na0.57Ca0.44)Σ1.01(Ba0.57K0.44)Σ1.01(Fe3.53Mn0.30Mg0.04Zn0.01)Σ3.88(Ti1.97Nb0.06Zr0.01)Σ2.04(Si3.97Al0.03O14)O2.00
(OH2.25F0.73O0.02)Σ3.00.
The Kola jinshajiangite differs from the original Chinese
sample in higher value of the Mn/Fe ratio and lower value of the Nb/Ti ratio and
lower F content. The Swedish mineral occupies intermediate position in its Mn/Fe
ratio.
In its chemical composition, bafertisite
from Gremyakha-Vyrmes is similar to bafertisite from its type locality, the
Bayan Obo alkaline complex,
Chemically, bafertisite and jinshajiangite from Kola differ
one from other not only in part of species-defining sodium and barium cations
but also in subordinate constituents. Bafertisite is characterized by higher content
of fluorine and lower content of niobium. Concentration of calcium in Kola bafertisite
is below detection limit whereas in our jinshajiangite, Ca, undoubtedly replacing
Na, is significant admixture.
Barium minerals were not found in the Gremyakha-Vyrmes
alkaline granites and their derivatives before (Polkanov et al., 1967; Bulakh, 1997). Ba was accumulated probably because of
its mobilization from potassium feldspar as a result of albitization of granite
interacted with feldspathoid rocks, namely nepheline syenites and ijolites.
This study was supported by grant of President
of Russain Federation No. 863.2008.5 and grant of Russian Science Support
Foundation (I.V.P.).
References:
Bulakh A.G. On the mineralogy of alkaline granites of
the Gremyakha Tundra,
Ganzeev A.A., Efimov A.F., Lyubomilova G.V. Manganese bafertisite
from Burpala massif (Northern Baikal Region) // Proc. of Fersman Mineralogical
Museum of AN USSR. 1971, vol. 20, p. 195-197 (in Russian).
Hong
Wenxing, Fu Pinqiu. Jinshajiangite ã a new
Ba-Mn-Fe-Ti-bearing silicate mineral // Geochemistry (
Kuan Ya-Hsien, Simonov V.I., Belov N.V. Crystal
structure of bafertisite, BaFe2TiO[Si2O7](OH)2
// Doklady AN USSR. 1963, vol. 149, µ 6, p. 1416-1419 (in Russian).
Polkanov A.A., Eliseev N.A., Eliseev E.N., Kavardin
G.I. ÁGremyakha-Vyrmes Massif on
Rastsvetaeva R.K., Chukanov N.V., Rozenberg K.A. Crystal
structure of Ájinshajiangite from Norra Karr
massif (
Semenov E.I., Chang Pei-Shan. New mineral bafertisite
// Science Record. 1959, vol. 3, µ 12, p. 652-655 (in Russian).