IMA 2018-007 = dalnegorskite

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Marco E. Ciriotti
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IMA 2018-007 = dalnegorskite

Messaggio da Marco E. Ciriotti » mer 07 ago, 2019 13:44

Referenza:
▪ Shchipalkina, N.V., Pekov, I.V., Ksenofontov, D.A., Chukanov, N.V., Belakovskiy, D.I., Koshlyakova, N.N. (2019): Dalnegorskite, Ca5Mn(Si3O9)2, a new pyroxenoid of the bustamite structure type, a rock-forming mineral of calcic skarns of the Dalnegorskoe boron deposit (Primorskiy kray, Russia). Zapiski RMO, 148(2), 61-75.

Abstract:
Dalnegorskite — the new pyroxenoid with the crystal-chemical formula Ca2Ca2MnCa(Si3O9)2, and the simplified formula Ca5Mn(Si3O9)2, is a rock-forming mineral in the boron-bearing calcareous skarns of the Dalnegorskoe boron-silicate deposit (Dalnegorsk, Primorsky Krai, Russia). It belongs to the structural type of bustamite and forms a continuous solid-solution series with the isostructural mineral ferrobustamite Ca2Ca2FeCa[Si3O9]2. These pyroxenoids form thinly-radiated banded beige, pinkish-white and milky-white aggregates typically consisting of split thin acicular to fiber-like individuals and are associated with hedenbergite, datolite, andradite, galena, sphalerite, and pyrrhotite. Dmeas. = 3.02(2), Dcalc. = 3.035 g·cm–3. Dalnegorskite is optically biaxial, negative, α = 1.640 (3), β = 1.647 (3), γ = 1.650 (3)°, 2Vmeas. = 75(10)º. The average chemical composition of the holotype (electron microprobe data) is: MgO 0.23, CaO 40.02, MnO 5.02, FeO 3.64, SiO2 50.65, total 99.56 wt.%. The empirical formula calculated on 18 O atoms is Ca5.03Mn0.51Fe0.36Mg0.04Si6.03O18. The crystal structure of the new mineral was refined by powder X-ray diffraction data using the Rietveld method, Rp = 0.0345, Rwp = 0.0444, R1 = 0.0790, wR2 = 0.0802. Dalnegorskite is triclinic, P-1, a = 7.2588(11), b = 7.8574(15), c = 7.8765(6) Å, α = 88.550(15), β = 62.582(15), γ = 76.621(6)º, V = 386.23(11) Å3, Z = 1. Dalnegorskite is distinctly different from the related mineral wollastonite in the infrared spectrum. The wave-numbers of maxima of strong bands in the characteristic region of Si—O stretching vibrations in the IR spectrum of dalnegorskite are (cm–1): 905, 937, 1025, 1070. The type specimen of dalnegorskite is deposited in the collection of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia (No. 96201).
Marco E. Ciriotti

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Marco E. Ciriotti
Messaggi: 25808
Iscritto il: ven 25 giu, 2004 11:31
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Re: IMA 2018-007 = dalnegorskite

Messaggio da Marco E. Ciriotti » mer 07 ago, 2019 14:55

Bustamite group (structural formulae)

Bustamite Ca2Ca2Mn2+Mn2+(Si3O9)2 tric P1 7.139 7.719 7.747 79.257 63.074 76.175 1 368
Dalnegorskite Ca2Ca2Mn2+Ca(Si3O9)2 tric P1 7.2588 7.8574 7.8765 88.550 62.582 76.621 1 386.23
Ferrobustamite Ca2Ca2Fe2+Ca(Si3O9)2 tric P1 7.253 7.862 7.900 79.23 62.117 76.710 1 385.9
Mendigite Mn2+2Mn2+2Mn2+Ca(Si3O9)2 tric P1 7.0993 7.6370 7.7037 79.58 62.62 76.47 1 359.29
Marco E. Ciriotti

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