A re-evaluation of stannopalladinite using modern analytical techniques

[Marco E. Ciriotti]

Prossima pubblicazione.

Referenza:
▪ Kasatkin, A.V., Vymazalová, A., Nestola, F., Gurzhiy, V.V., Agakhanov, A.A., Škoda, R., Belakovskiy, D.I., Generalov, M.E. (2023): A re-evaluation of stannopalladinite using modern analytical techniques. Mineralogical Magazine, 87, (in press).

Abstract:
The investigation of the sample 41647 from the Platinum Placer of Ugol’nyi Ruchei, Norilsk Cu-Ni deposit, Russia, stored in the systematic collection of the Fersman Mineralogical Museum, revealed that it contained the mineral which can be identified as the original stannopalladinite described in 1947. Since the literature information on the latter is controversial, the mineral was re-studied using modern analytical techniques.
Stannopalladinite occurs as spherical and ovoid-shaped grains up to 0.08 mm closely intergrown with tetraferroplatinum as part of flattened, prismatic crystals up to 6 mm long. The micro-indentation hardness of stannopalladinite (VHN, 30 g load) is 244 kg/mm2 (range 233–266, n = 4), corresponding to a Mohs hardness of 4. The calculated density is 9.781 g/cm3. In reflected light, stannopalladinite is pale pink. The bireflectance is noticeable only in oil immersion. In crossed nicols the mineral exhibits strong anisotropy with color effects changing from reddish purple to greyish blue and polysynthetic twinning of grains. The reflectance curves show distinct anomalous dispersion. The chemical composition (wt.%, electron microprobe data, mean of 11 analyses) is: Cu 8.48, Pd 61.21, Pt 0.89, Sn 25.87, Pb 3.70, total 100.15. The empirical formula calculated on the basis of 4 atoms pfu is (Pd2.42Cu0.56Pt0.02)Σ3.00(Sn0.92Pb0.08)Σ1.00. The ideal chemical formula of stannopalladinite is therefore proposed as (Pd,Cu)3Sn instead of Pd3Sn2 used in the Official IMA List of Minerals. The strongest powder X-ray diffraction lines are [dobs, Å (I, %) (hkl) ]: 2.292 (42) (231), 2.166 (100) (331), 2.034 (10) (710), 1.916 (15) (141), 1.851 (15) (630). The powder X-ray data are indexed in the orthorhombic unit cell with a = 14.634(2), b = 8.5253(6), c = 4.5946(3) Å, V = 573.24(7) Å3 (Z = 8). Stannopalladinite can be reliably identified among all other minerals belonging to the binary Pd-Sn and ternary Pd-Cu-Sn systems by a combination of chemical, optical and X-ray data.

[Marco E. Ciriotti]

In assenza di dati strutturali l'interessante lavoro di Kasatkin et al. (2023) non può considerarsi una formale (IMA accepted) ridefinizione della stannopalladinite.

Il materiale della località-tipo si direbbe comunque molto ben ri-valutato.

Una breve disamina sulle problematiche e le difficoltà inerenti l'impossibilità di avere X-ray dati che permettano di determinare (raffinare) le strutture di molte specie minerali è in un prossimo articolo che sarà pubblicato in Micro 4/2023 (in distribuzione nella prima metà di dicembre 2023).

Al giorno d'oggi per circa 950 minerali, pari a circa il 15% delle specie riconosciute come valide dall'IMA CNMNC, la struttura cristallina non è mai stata determinata ed è quindi non nota.

[Marco E. Ciriotti]

Pubblicazione effettuata.

Referenza:
▪ Kasatkin, A.V., Vymazalová, A., Nestola, F., Gurzhiy, V.V., Agakhanov, A.A., Škoda, R., Belakovskiy, D.I., Generalov, M.E. (2023): A re-evaluation of stannopalladinite using modern analytical techniques. Mineralogical Magazine, 87, 773-782.