In:
Mineralogical Magazine, Mineralogical Society
Abstract:
The new mineral mazorite, ideally Ba 3 (PO 4 ) 2 , a P-analogue of gurimite Ba 3 (VO 4 ) 2 , was discovered in rankinite paralava hosted by the massive gehlenite-bearing pyrometamorphic rocks of the Hatrurim Complex in Israel. It has also recently been discovered in xenolith samples from the Bellerberg volcano in Germany. Holotype mazorite usually forms colourless plate-like crystals up to 70–100 μm in length but also occurs in small aggregates in association with other rare Ba-bearing minerals such as zadovite, celsian, hexacelsian, bennesherite, sanbornite, walstromite, fresnoite, gurimite, alforsite and barioferrite. The mineral is transparent, exhibits vitreous lustre and has a good cleavage on (001). Optically, mazorite is uniaxial (+), with ω = 1.760(3) and ɛ = 1.766(3) (λ = 589 nm). The empirical formula of the holotype mazorite calculated on 8O is (Ba 2.69 K 0.22 Na 0.04 Ca 0.02 Sr 0.01 ) Σ2.98 (P 1.16 V 0.57 S 0.24 Al 0.04 Si 0.03 ) Σ2.04 O 8 . Mazorite crystallises in space group R $\bar{3}$ m , with unit-cell parameters a = 5.6617(5) Å, c = 21.1696(17) Å, V = 587.68(9) Å 3 and Z = 3. Its crystal structure consists of BaO 12 , BaO 10 , and PO 4 polyhedra, ordered along the c -axis in PO 4 –BaO 10 –BaO 12 –BaO 10 –PO 4 columnar arrangement characteristic for palmierite-supergroup minerals. A tetrahedrally coordinated site is generally occupied by P 5+ but can be partially substituted by V 5+ and S 6+ . This substitution is shown in the Raman spectrum of mazorite, which reveals bands that can be assigned to the stretching and bending vibrations of (PO 4 ) 3– , (VO 4 ) 3– and (SO 4 ) 2– groups. The Raman spectra of mazorite from two localities (Hatrurim and Bellerberg) and spectra of minerals belonging to the mazorite Ba 3 (PO 4 ) 2 to gurimite Ba 3 (VO 4 ) 2 solid-solution series are presented. The gradual shift of the Raman bands, caused by cation substitutions, is well observed. The high V 5+ → P 5+ substitution is also observed for gurimite, for which the first X-ray structural data are also presented. Mazorite and other Ba-bearing minerals crystallised from a small portion of residual melt enriched in incompatible elements, such as Ba, V, P, U, S, Ti and Nb, at a temperature of ~1000°C.
Type of Medium:
Online Resource
ISSN:
0026-461X
,
1471-8022
Language:
English
Publisher:
Mineralogical Society
Publication Date:
2023
detail.hit.zdb_id:
2034522-7
SSG:
13
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