Saranovskite, SrCaFe2+2(Cr4Ti2)Ti12O38, a new crichtonite-group mineral

• Published in: Physics and chemistry of minerals Vol. 47; no. 11
• Main Authors: Chukanov, Nikita V., Rastsvetaeva, Ramiza K., Kazheva, Olga N., Ivanov, Oleg K., Pekov, Igor V., Agakhanov, Atali A., Van, Konstantin V., Shcherbakov, Vasiliy D., Britvin, Sergey N.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-11-2020; Springer Nature B.V
• Subjects: Aluminum oxide; Barium oxides; Calcite; Cations; Chemical composition; Chromite; Clinochlore; Crystal structure; Crystallography and Scattering Methods; Crystals; Diffraction patterns; Earth and Environmental Science; Earth Sciences; Electron probes; Geochemistry; Iron oxides; Lanthanum oxides; Mineral Resources; Mineralogy; Original Paper; Praseodymium oxide; Scandium oxides; Scratch hardness; Single crystals; Titanium dioxide; X ray powder diffraction; X-ray diffraction; Yttrium oxide; Zirconium dioxide; Saranovskite; Glavnoe Saranovskoe deposit; New mineral; Raman spectroscopy; IR spectroscopy; Middle urals; Crichtonite group; Crystal structure
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-020-01119-1

The new crichtonite-group mineral saranovskite, ideally SrCaFe
2+
2
(Cr
4
Ti
2
)Ti
12
O
38
, was discovered in the Glavnoe Saranovskoe deposit, Middle Urals, Russia, and named after the type locality. The associated minerals are chromite, Cr-bearing clinochlore, and calcite. Saranovskite forms black crude equant crystals about 2 mm across. The lustre is submetallic, and the streak is brownish-gray. Cleavage is not observed. The Mohs hardness is 6. Density calculated using the empirical formula is equal to 4.501 g cm
–3
. The reflectance spectra in visible range are given. The IR spectrum shows the absence of H-, B- and C-bearing groups. The Raman spectrum of saranovskite confirms the absence of H-bearing groups and indicates a rather high degree of ordering of Ti
4+
and lower-valence cations. The chemical composition of saranovskite is (wt.%; electron microprobe, total iron apportioned between FeO and Fe
2
O
3
taking into account charge balance): MgO 2.01, CaO 1.43, MnO 0.21, FeO 8.14, SrO 3.27, BaO 2.18, Al
2
O
3
0.53, Sc
2
O
3
0.69, Cr
2
O
3
10.27, Fe
2
O
3
2.19, Y
2
O
3
1.56, La
2
O
3
0.94, Ce
2
O
3
0.91, Pr
2
O
3
0.14, Nd
2
O
3
0.35, TiO
2
64.25, ZrO
2
0.58, total 99.65. The crystal chemical formula of saranovskite is (Sr
0.55
Ba
0.25
Ln
0.10
Ca
0.10
)(Ca
0.36
Y
0.25
Ln
0.16
Fe
2+
0.08
Zr
0.10
Mn
0.05
) (Fe
2+
1.12
Mg
0.88
)(Cr
3+
2.34
Ti
2.28
Fe
2+
0.91
Fe
3+
0.11
Al
0.18
Sc
3+
0.18
)(Ti
5.82
Fe
3+
0.18
)Ti
6.0
O
38
. The idealized formula is SrCaFe
2+
2
(Cr
4
Ti
2
)Ti
12
O
38
. The crystal structure was determined using single-crystal X-ray diffraction data and refined to
R
 = 0.0243. The new mineral is isostructural to other crichtonite-group members. Saranovskite is trigonal, space group
R
3
¯
, with
a
 = 10.3553(2) Å,
c
 = 20.7301(4) Å,
V
 = 1925.12(8) Å
3
and
Z
 = 3. The strongest lines of the powder X-ray diffraction pattern [
d,
Å (
I
, %) (
hkl
)] are: 3.398 (75) (024), 2.881 (100) (– 126), 2.842 (65) (– 234), 2.247 (67) (– 144). 2.137 (76) (– 345), 1.799 (63) (– 348), 1.597 (72) (– 1.4.10, 152), 1.439 (76) (520).