IMA 2018-049 = antofagastaite

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Marco E. Ciriotti
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IMA 2018-049 = antofagastaite

Messaggio da Marco E. Ciriotti » dom 14 apr, 2019 12:14

Prossima pubblicazione.

Referenza:
▪ Pekov, I.V., Kovrugin, V.M., Siidra, O.I., Chukanov, N.V., Belakovskiy, D.I., Koshlyakova, N.N., Yapaskurt, V.O., Turchkova, A.G., Möhn, G. (2019): Antofagastaite, Na2Ca(SO4)2·1.5H2O, a new mineral related to syngenite. Mineralogical Magazine, 83, (in press).

Abstract:
The new mineral antofagastaite, ideally Na2Ca(SO4)2·1.5H2O, was found in the oxidation zone of sulfide-quartz veins at the abandoned Coronel Manuel Rodríguez mine, Mejillones, Antofagasta province, Antofagasta region, Chile. It is associated with sideronatrite, metasideronatrite, aubertite, gypsum, ferrinatrite, glauberite, amarillite and an unidentified Fe phosphate. Antofagastaite occurs as prismatic crystals up to 0.5 × 1 × 5 mm3, elongated along [010], typically combined in open-work aggregates up to 1 cm across. Antofagastaite is transparent, colourless, with vitreous lustre. It is brittle, the oh ’ hardness is ca 3. Cleavage is distinct on (001). Dmeas is 2.42(1) and Dcalc is 2.465 g·cm–3. Antofagastaite is optically biaxial (–), α 1.489(2), β 1.508(2), γ 1.510(2), 2Vmeas. 40(10)°. IR spectrum is reported. Chemical composition (wt%, electron microprobe, H2O determined by gas chromatography) is: Na2O 20.85, CaO 17.42, SO3 52.56, H2O 7.93, total 98.76. The empirical formula (based on 8 O atoms belonging to sulfate anions pfu, with all H belonging to H2O molecules) is Na2.06Ca0.95S2.01O8·1.35H2O. Antofagastaite is monoclinic, P21/m, a 6.4596(4), b 6.8703(5), c 9. 685( ) Å β 0 .580( )° V 406.67(5) Å3 and Z 2. The strongest reflections of the powder XRD pattern [d, Å (I, %) (hkl)] are: 9.17 (100) (001), 5.501 (57) (011), 3.437 (59) (020), 3.058 (43) (003), 2.918 (50) (–211), 2.795 (35) (013) and 2.753 (50) (121, 201). The crystal structure was solved based on single-crystal XRD data, R1 = 5.71%. The structure of antofagastaite consists of ordered and disordered blocks. In terms of the crystal structure, the mineral is generally related to syngenite K2Ca(SO4)2·H2O. Incorporation of additional H2O molecules in the syngenite-type structure results in disorder of the one of the two tetrahedral sulfate groups occurring in antofagastaite. Besides the above-reported type material, antofagastaite together with syngenite and blödite occurs in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia.
Marco E. Ciriotti

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Marco E. Ciriotti
Messaggi: 25332
Iscritto il: ven 25 giu, 2004 11:31
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Re: IMA 2018-049 = antofagastaite

Messaggio da Marco E. Ciriotti » lun 15 apr, 2019 11:51

syngenite group

Antofagastaite Na2Ca(SO4)2·1.5H2O mon P21/m 6.4596 6.8703 9.4685 90.00 104.580 90.00 2 406.67
Koktaite (NH4)2Ca(SO4)2·H2O mon P21/m 6.34 7.15 10.17 90.00 102.7 90.00 2 449.65
Syngenite K2Ca(SO4)2·H2O mon P21/m 6.2469 7.1449 9.7710 90.00 104.0 90.00 2 423.02
Marco E. Ciriotti

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