IMA 2016-075 = fluorarrojadite-(BaNa)

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Marco E. Ciriotti
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IMA 2016-075 = fluorarrojadite-(BaNa)

Messaggio da Marco E. Ciriotti » sab 21 ott, 2017 13:15

Prossima pubblicazione.

▪ ŠtevKo, M., Sejkora, J., Uher, P., Cámara, F., Škoda, R., Vaculovič, T. (2017): Fluorarrojadite-(BaNa), BaNa4CaFe13Al(PO4)11(PO3OH)F2, a new member of the arrojadite group from Gemerská Poloma, Slovakia. Mineralogical Magazine, 81, (in press).

The new mineral fluorarrojadite-(BaNa), ideally BaNa4CaFe13Al(PO4)11(PO3OH)F2 was found on the dump of of Elisabeth adit near Gemerská Poloma, Slovakia. It occurs in hydrothermal quartz veins intersecting highly fractionated, topaz-zinnwaldite S-type leucogranite. Fluorarrojadite-(BaNa) is associated with fluorapatite, “fluordickinsonite-(BaNa)”, triplite, viitaniemiite and minor amounts of other minerals. It forms fine grained irregular aggregates up to 4 x 2 cm, which consists of individual anhedral grains up to 0.01 mm in size. It has a yellowish-brown to greenish-yellow colour, very pale yellow streak, a vitreous to greasy lustre. Mohs hardness is about 4½ to 5. The fracture is irregular and the tenacity is brittle. The measured density is 3.61(2) g·cm-3 and calculated density is 3.650 g·cm-3. Fluorarrojadite-(BaNa) is biaxial (+) and nonpleochroic. The calculated efractive index based on empirical formula is 1.674. The empirical formula (based on 47 O and 3 (OH+F) apfu) is A1(Ba0.65K0.35)Σ1.00 A2Na0.35 B1(Na0.54Fe0.46)Σ1.00 B2Na0.54Ca(Ca0.74Sr0.20Pb0.02Ba0.04) Σ1.00Na2Na3Na0.46M(Fe7.16Mn5.17Li0.37Mg0.12Sc0.08Zn0.06Ga0.02Ti0.02)Σ13.00Al1.02P11O44PO3.46(OH)0.54W(F1.54OH0.46). Fluorarrojadite-(BaNa) is monoclinic, space group Cc, a = 16.563(1) Å, b = 10.0476(6) Å, c = 24.669(1) Å, β = 105.452(4)°, V = 3957.5(4) Å3 and Z = 4. The seven strongest reflections in the powder X-ray diffraction pattern are [dobs in Å, (I), hkl]: 3.412, (21), 116; 3.224, (37), 206; 3.040, (100), 42-4; 2.8499, (22), 33-2; 2.7135, (56), 226; 2.5563, (33), 028 and 424; 2.5117, (23), 040. The new mineral is named according to the actual nomenclature scheme of arrojadite group minerals, which was approved by the CNMNC IMA. In fluorarrojadite-(BaNa) Fe2+ is a dominant cation at the M site (so the root-name is arrojadite) and two suffixes are added to the root-name according to the dominant cation of the dominant valence state at the A1 (Ba2+) and B1 sites (Na+). A prefix fluor is added to the root-name as F- is dominant over (OH)- at the W site.
Marco E. Ciriotti

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