Ca-bearing nepheline found in the Kajishiyama basanite, Tsuyama Basin, southwest Japan, was investigated to clarify its genesis in silica-undersaturated magmas. The basanite contains olivine and augite as phenocrysts and microphenocrysts, with Ca-bearing nepheline, olivine, augite, ulvöspinel, plagioclase, alkali feldspar, apatite and zeolites in the groundmass. Zeolites are more abundant in coarser-grained samples. The whole-rock composition of the basanite is characterised by low SiO2 and P2O5 contents and high total Fe, MgO, Na2O, K2O, Ba and Sr contents.

The Ca-bearing nepheline, ~20 μm in size, occurs in the mesostasis of the Kajishiyama basanite and contains up to 2.31 wt.% CaO and 16.75 wt.% Na2O, in contrast to nepheline from the Hamada nephelinite, southwest Japan. The approximate compositional formula of the Kajishiyama nepheline with the highest Ca content is (Ca0.467Ba0.013Na5.286K0.919□Total1.385)Σ8.070(Si0.912Al6.980Cr3+0.003Fe3+0.067 Mg0.017)Σ7.979Si8.000O32; i.e. Ne65.50Ks11.39Qxs11.22CaNe11.89.

Basanites are defined as being nepheline-normative, however they are high in normative plagioclase, the amount of which increases with fractionation of the magma. Nepheline crystallised after plagioclase, at the last stage of magmatic solidification is enriched in Ca. Such Ca-rich nepheline only forms from a magma which is high in normative plagioclase, as is the case in the Kajishiyama basanite. In contrast, Ca-poor nepheline is precipitated from nephelinitic magmas that crystallise melilite instead of plagioclase, even when Ca contents are high.

A new occurrence of austinite, CaZnAsO4(OH), conichalcite, CaCuAsO4(OH), and zincolivenite, CuZnAsO4(OH), is described from the Tripi mine, Peloritani Mountains, Sicily, Italy. These species have been observed in euhedral crystals in vugs of a calcite vein and were characterised using single-crystal X-ray diffraction, electron microprobe analysis and micro-Raman spectroscopy. Austinite and conichalcite have isotypic relations, both crystallising in space group P212121. Unit-cell parameters of austinite are a = 7.4931(5), b = 9.0256(6), c = 5.9155(4) Å, V = 400.06(5) Å3; its crystal structure was refined on the basis of 1210 unique reflections with Fo > 4σ(Fo) and 77 least-square parameters to R1 = 0.0236. Conichalcite has unit-cell parameters a = 7.419(10), b = 9.111(11), c = 5.867(7) Å and V = 396.6(1.4) Å3; the diffraction quality of its available grains was not good enough to allow a high-quality structural refinement. Chemical formulae of austinite and conichalcite are Ca1.04(1)Zn0.86(4)Cu0.09(4)As0.98(2)P0.02(1)O4(OH)0.98 and Ca0.98(1)Fe2+0.02(4)Cu0.69(10)Zn0.30(6)As0.97(2)P0.03(1)O4(OH)0.98, respectively. The new chemical data on the austinite–conichalcite isotypic pair, coupled with previous analyses, supports a possible miscibility gap between the compositions (Zn0.25Cu0.75) and (Zn0.50Cu0.50). Zincolivenite has unit-cell parameters a = 8.4594(9), b = 8.5324(8), c = 5.9893(6) Å, V = 432.30(12) Å3 and space group Pnnm; its crystal structure was refined to R1 = 0.0230 for 523 unique reflections with Fo > 4σ(Fo) and 47 least-square parameters. Its chemical composition is Cu0.73(5)Zn1.25(5)As1.01(1)O4(OH)1.01. The refinement of the crystal structure supports the ordering of Cu and Zn in two different crystallographic sites. Micro-Raman spectra of austinite, conichalcite and zincolivenite are discussed, with a focus on the O–H stretching region where local Zn and Cu arrangements affect the position of Raman bands in zincolivenite. These arsenates probably play an environmental role in the Peloritani area, where the occurrence of high contents of some potentially toxic elements in soils and stream sediments has been reported.

Vrančiceite is a new mineral species discovered in a sample collected from the old mine dumps of the abandoned Vrančice deposit near Příbram, central Bohemia, Czech Republic. Vrančiceite occurs as rare anhedral grains, up to 100 μm in size, in a calcite gangue, associated with cinnabar, djurleite, galena and hedyphane. Vrančiceite is black, with metallic lustre. Mohs hardness is ca. 2–3, calculated density is 6.652 g.cm–3. In reflected light, vrančiceite is light grey with a yellowish shade; bireflectance, pleochroism and anisotropy are all weak. Internal reflections were not observed. Reflectance values for the four Commission on Ore Mineralogy wavelengths of vrančiceite in air [Rmax, Rmin (%) (λ in nm)] are: 33.6, 31.2 (470); 33.9, 30.6 (546); 31.1, 30.0 (589); and 32.1, 29.1 (650). The empirical formula, based on electron-microprobe analyses, is Cu10.11(4)Ag0.01(1)Hg2.87(4)Sb0.01(1)Bi0.01(1)S7.99(8). The ideal formula is Cu10Hg3S8 (Z = 2), which requires (in wt.%) Cu 42.54, Hg 40.29 and S 17.17, total 100.00. Vrančiceite is triclinic, P$\bar{1}$, with unit-cell parameters a = 7.9681(2), b = 9.7452(3), c = 10.0710(3) Å, α = 77.759(1), β = 76.990(1), γ = 79.422(1)°, V = 737.01(4) Å3 and Z = 2. The strongest reflections of the calculated powder X-ray diffraction pattern [d, Å (I) hkl] are: 3.354 (76) $\bar{2}$01, 3.111 (68) 222, 2.833 (100) 213, 2.733 (93) 231, 2.705 (76) 2$\bar{2}$1 and 2.647 (71) $\bar{2}\bar{1}$2. According to the single-crystal X-ray diffraction data (R1 = 0.0262), the crystal structure of vrančiceite can be described as comprising Cu–S layers, connected through CuS3 polyhedra, giving rise to a three-dimensional framework with channels running along the a axis and hosting linearly coordinated Hg atoms. Structural relations with gortdrumite are discussed. Vrančiceite is named after its type locality, the Vrančice deposit near Příbram. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2022–114).

The new mineral mazorite, ideally Ba3(PO4)2, a P-analogue of gurimite Ba3(VO4)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 (Ba2.69K0.22Na0.04Ca0.02Sr0.01)Σ2.98(P1.16V0.57S0.24Al0.04Si0.03)Σ2.04O8. 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) Å3 and Z = 3. Its crystal structure consists of BaO12, BaO10, and PO4 polyhedra, ordered along the c-axis in PO4–BaO10–BaO12–BaO10–PO4 columnar arrangement characteristic for palmierite-supergroup minerals. A tetrahedrally coordinated site is generally occupied by P5+ but can be partially substituted by V5+ and S6+. This substitution is shown in the Raman spectrum of mazorite, which reveals bands that can be assigned to the stretching and bending vibrations of (PO4)3–, (VO4)3– and (SO4)2– groups. The Raman spectra of mazorite from two localities (Hatrurim and Bellerberg) and spectra of minerals belonging to the mazorite Ba3(PO4)2 to gurimite Ba3(VO4)2 solid-solution series are presented. The gradual shift of the Raman bands, caused by cation substitutions, is well observed. The high V5+ → P5+ 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.

The palmierite supergroup, approved by the IMA-CNMNC, includes five mineral species characterised by the general crystal-chemical formula XIIM1XM22(IVTO4)2 (Z = 3). On the basis of the crystal-chemical arguments and heterovalent isomorphic substitution scheme M++T6+ ↔ M2++T5+, the palmierite supergroup can be formally divided into two groups: the palmierite group M12+M22+(T6+O4)2, and the tuite group M12+M222+(T5+O4)2. Currently, the palmierite group includes palmierite K2Pb(SO4)2, and kalistrontite K2Sr(SO4)2, whereas the tuite group combines tuite Ca3(PO4)2, mazorite Ba3(PO4)2, and gurimite Ba3(VO4)2. The isostructural supergroup members crystallise in space group R$\bar{3}$m (no. 166). The palmierite-type crystal structure is characterised by a sheet arrangement composed of layers formed by M1O12 and M2O10 polyhedra separated by TO4 tetrahedra perpendicular to the c axis. The abundance of distinct ions, which may be hosted at the M and T sites (M = K, Na, Ca, Sr, Ba, Sr, Pb, Rb, Zn, Tl, Cs, Bi, NH4 and REE; T = Si, P, V, As, S, Se, Mo, Cr and W) implies many possible combinations, resulting in potentially new mineral species. Minerals belonging to the palmierite supergroup are relatively rare and usually form under specific conditions, and their synthetic counterparts play a significant role in various industrial applications.

The new mineral bakakinite, ideally Ca2V2O7, was found in the high-temperature (not lower than 500°C) exhalations of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with anhydrite, svabite, pliniusite, schäferite, berzeliite, diopside, hematite, powellite, baryte, fluorapatite, calciojohillerite, ludwigite, magnesioferrite, anorthite, titanite and esseneite. Bakakinite forms flattened crystals up to 30 × 5 μm, typically distorted. The mineral is transparent, colourless or pale yellow, with strong vitreous lustre. Electron microprobe analysis gave (wt.%): CaO 37.04, SrO 0.26, SiO2 0.16, P2O5 1.48, V2O5 49.47, As2O5 10.85, SO3 0.35, total 99.61. The empirical formula calculated on the basis of 7 O apfu is (Ca1.99Sr0.01)Σ2.00(V1.64As0.28P0.06Si0.01S0.01)Σ2.00O7. The Dcalc is 3.463 g cm–3. Bakakinite is triclinic, P$\bar{1}$, unit-cell parameters are: a = 6.64(2), b = 6.92(2), c = 7.01(2) Å, α = 86.59(7), β = 63.77(7), γ = 83.47(6)°, V = 287.0(5) Å3 and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 4.647(27)(111, 0$\bar{1}$1), 3.138(76)(002), 3.103(100)(120, 121), 3.027(20)(021), 2.960(81)(200), 2.158(19)(031, 302), 1.791(16)(320), 1.682(16)(114) and 1.584(17)(1$\bar{3}$3, 403). Bakakinite is a natural analogue of synthetic Ca2V2O7. The mineral is named in honour of the outstanding Russian crystallographer and crystal chemist Vladimir Vasilievich Bakakin (born 1933).

We investigated the compositions of a suite of 361 chrome-bearing spinels from spinel peridotites, ophiolitic mantle chromitites and from layered igneous intrusions in which the Fe2+/Fe3+ ratio has been determined by Mössbauer spectroscopy. We explore the crystal-chemical controls on the distribution of Fe3+ and on mineral stoichiometry with regard to electron-probe correction procedures for estimating Fe3+ in spinel. We find that chrome-bearing spinels can be subdivided into three groups: a Cr–Al-rich group; a high-Fe group; and a highly oxidised group. Spinels of the Cr–Al group are found in spinel peridotites and ophiolitic mantle chromitites. They are normal spinels with a low Fe3+ content and compositions that are close to stoichiometric. Spinels in the high-Fe group are found in layered igneous intrusions. They are also normal spinels which have higher concentrations of Fe3+ on the octahedrally coordinated site than is found for the Cr–Al group. Stoichiometric calculations tend to overestimate the Fe3+ content and their compositions do not conform to the MgO–cr# correlation found in the Cr–Al group. Spinels in the highly oxidised group are found in layered intrusions and ophiolitic mantle chromitites. They have (Fe3+/ΣFe)Möss > 0.4 and high Cr (cr# > 0.5), but relatively low Fe2+ (fe# 0.24–0.56). Stoichiometric calculations tend to underestimate the Fe3+ content. They represent normal spinels in which tetrahedrally coordinated Fe2+ has been oxidised to Fe3+.

Our data show that spinels with greater Cr and Fe are sufficiently different in their crystal chemistry from the aluminous spinels to indicate that the EPMA correction procedures developed for Fe3+ in aluminous spinels on the basis of the Cr/Al ratio, and used in oxy-thermobarometry, are inappropriate for Cr-rich and Fe-rich compositions.

Napoliite, ideally Pb2OFCl, is a new fluoroxychloride mineral found in a specimen from a fumarole formed subsequent to the 1944 eruption of Vesuvius volcano, Naples Province, Italy. It occurs as well-shaped lamellar crystals up to 0.25 × 0.25 × 0.01 mm typically forming clusters up to 0.4 × 0.4 mm on the surface of volcanic scoria in association with anglesite, artroeite, atacamite, calcioaravaipaite, cerussite, challacolloite, cotunnite, hephaistosite, manuelarossiite, matlockite and susannite. Napoliite is colourless with white streak and adamantine lustre. It is brittle and has a laminated fracture. Cleavage is perfect on {001}. Dcalc = 7.797 g cm–3. The calculated mean refractive index is 2.10. Chemical composition (wt.%, electron microprobe) is: PbO 91.71, F 3.89, Cl 7.34, –O=(F+Cl) –3.30, total 99.64. The empirical formula calculated on the basis of 3 anions is Pb1.999O0.997F0.996Cl1.007. Raman spectroscopy confirms the absence of OH– groups and H2O molecules in the mineral. Napoliite is tetragonal, space group P42/mcm, a = 5.7418(11), c = 12.524(4) Å, V = 412.9(2) Å3 and Z = 4. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 3.860 (85) (111); 3.139 (20) (004); 2.914 (100) (113); 2.866 (63) (200); 2.118 (19) (204); 2.027 (19) (220); 1.665 (20) (313); and 1.642 (23) (117). The crystal structure was refined to R1 = 0.024 for 222 reflections with F > 4σ(F). It is based on lead oxide blocks derived from that of litharge PbO, which alternate with layers of chloride ions. Napoliite represents a new structure type with a unique order/disorder pattern of fluorine and oxygen atoms. The new mineral is dimorphous with rumseyite. It is named after the city of Naples (Napoli in Italian).

Oxy-dravite, ideally Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3(O), was found in a composition near its ideal end-member at the Beluga occurrence, Nunavut territory, Canada. It occurs in retrograde albite–muscovite–corundum–calcite domains in a calc-silicate rock. This uncommon oxy-dravite occurs as dark brown, equant to short-prismatic, idiomorphic crystals with vitreous lustre and up to ca. 4 × 3 cm in size. The oxy-dravite is optically uniaxial (–), with ω = 1.6453(5) and ɛ = 1.6074(18); its calculated density is 3.069 g.cm–3 with a compatibility index of 0.016. The Beluga oxy-dravite has trigonal symmetry, space group R3m with a = 15.9121(2) Å, c = 7.1788(10) Å, V = 1574.12(5) Å3 and Z = 3. The crystal structure was refined to R1 = 1.45 using 1613 unique reflections. The empirical crystal-chemical formula is X(Na0.88Ca0.08□0.03K0.01)Y(Al1.49Mg1.31Fe0.15Ti0.04Zn0.01)Z(Al5.42Mg0.58)T(Si5.84Al0.16O18)B(BO3)3V(OH2.95O0.05)W(O0.84OH0.01F0.15).

Oxy-dravite in nature commonly occurs in a solid solution with foitite, schorl and oxy-schorl. At the Beluga occurrence, its minor contents of Al, vacancy [□], and Ca are most likely compensated by (□Al)(NaR2+)–1 and (CaMg)(NaAl)–1 exchanges of the oxy-magnesio-foitite and magnesio-lucchesiite components. The Beluga occurrence of oxy-dravite is characterised by an Mg-rich environment related to a metamorphic overprint of the original sedimentary sequence. This sequence of marine dolomitic argillaceous marl was influenced by (B,Cl)-rich fluids, probably proximally-derived from mineral breakdown reactions in the calc-silicate during the retrograde stage of metamorphism. The locality is a rare example of a tourmaline + corundum assemblage.

Fluorbritholite-(Nd), ideally Ca2Nd3(SiO4)3F, has been approved by the International Mineralogical Association (IMA2023–001) and constitutes a new member of the britholite group of the apatite supergroup. It occurs in skarn from the Malmkärra iron mine, Norberg, Västmanland (one of the Bastnäs-type deposits in Sweden), associated with calcite, dolomite, magnetite, lizardite, talc, fluorite, baryte, scheelite, gadolinite-(Nd) and other REE minerals. Fluorbritholite-(Nd) forms anhedral and small grains, rarely up to 250 μm across. They are brownish pink and transparent with a vitreous to greasy lustre. The mineral is brittle, with an uneven or subconchoidal fracture and lacks a cleavage. In thin section, the mineral is nonpleochroic, uniaxial (–). Dcalc = 4.92(1) g⋅cm−3 and ncalc = 1.795. The empirical chemical formula from electron microprobe (WDS) point analyses is (Ca1.62Nd0.97Ce0.83Y0.52Sm0.30Gd0.23Pr0.17La0.16Dy0.11Er0.03Tb0.03Ho0.01Yb0.01)Σ4.99(Si2.92P0.08As0.01)Σ3.01O12.00[O0.48F0.26(OH)0.14Cl0.10Br0.02]Σ1.00. The crystal structure of fluorbritholite-(Nd) was refined from single-crystal X-ray diffraction data to R1= 0.043 for 704 unique reflections. It belongs to the hexagonal system, space group P63/m, with unit cell parameters a = 9.5994(3), c = 6.9892(4) Å and V = 557.76(5) Å3 for Z = 2. Fluorbritholite-(Nd) and other britholite-group minerals are a major sink for neodymium in REE-bearing skarns of Bastnäs type.

Minasgeraisite-(Y) is discredited on the basis of it being an ordered intermediate between datolite and hingganite-(Y) (IMA-CNMNC Proposal 23-F). An idealised formula is (Ca2Y2)□2(Be2B2)Si4O16(OH)4, which corresponds to Ca2□B2Si2O8(OH)2 (datolite) + Y2□Be2Si2O8(OH)2 (hingganite-(Y)). The type material is rich in Bi, the Bi-richest portion yet discovered from the type locality is shown to be an intermediate member between datolite, hingganite-(Y) and a hypothetical end-member phase yet to be found of composition Bi2□Be2Si2O8(OH)2. Minasgeraisite-(Y) has a different space group to datolite and hingganite-(Y). This lowering of symmetry to an acentric triclinic system is caused by different element occupancies on the A site of the gadolinite supergroup structure, which for minasgeraisite-(Y) becomes four individual sites. Such an order–disorder of elements is not considered as species-defining criteria despite the change in space group. Therefore, minasgeraisite-(Y) is discredited.

Aluminotaipingite-(CeCa), (Ce6Ca3)Al(SiO4)3[SiO3(OH)]4F3, is a new member of the cerite-supergroup minerals, whose general chemical formula is A9XM[TO3Ø]7Z3, (A = REE, Ca, Sr, Na and □; X = □, Ca, Na and Fe2+; M = Mg, Fe2+, Fe3+, Al and Mn; T = Si and P; Ø = O and OH; Z = □, OH and F). It was found in cavities of a leucogranitic orthogneiss at the Casette quarry, Montoso, Bagnolo Piemonte, Cuneo Province, Piedmont, Italy. Crystals of aluminotaipingite-(CeCa) are light pink to pink, transparent or semi-transparent, with a vitreous lustre. It forms pyramidal crystals up to 0.07 mm in size and observed forms are {0 0 1}, {1 0 $\bar{2}$}. The tenacity is brittle, no distinct cleavage is observed and the fracture is uneven. The mineral does not fluoresce in long- or short-wave ultraviolet light. The streak is white. Hardness (Mohs) = 5. The calculated density is 4.476 g cm–3.

The mineral is trigonal, space group R3c, with a = 10.658(3), c = 37.865(9) Å, V = 3725(2) Å3 and Z = 6. The eight strongest powder X-ray diffraction lines are [dobs, Å (I, %) (h k l)]: 8.38(29)(0 1 2), 4.499(28)(2 0 2), 3.282(41)(2 1 4), 2.936(100)(0 2 10), 2.816(51)(1 2 8), 2.669(37)(2 2 0), 2.207 (29)(3 0 12) and 1.935(35)(2 3 8). The structure was refined to R =0.0306 for 2297 reflections with I >2σ(I). The crystal structure of aluminotaipingite-(CeCa) contains two nine-fold coordinated sites (A1 and A2), which are occupied mainly by lanthanides, and a third nine-fold coordinated A3 site containing almost equal amounts of lanthanides and Ca. The X site is vacant and at the octahedral M site aluminium prevails over Fe3+. Among the three independent T sites, T2 belongs to a (SiO4)4– anion, whereas T1 and T3 belong to (SiO3OH)3– anions. Fluorine is involved in coordination with the A1 and A3 sites.

This work describes the mineralogy of dolomite carbonatite occurring at the Newania carbonatite complex, Rajasthan, north-western India. The mineralogy records the textural and compositional features of magmatic and post-magmatic stages of carbonatite evolution. Ferroan dolomite is the principal constituent and displays variable degrees of deformation, ranging from brittle-to-ductile deformation regimes. Apatite exhibits textural and compositional evolutionary trends from early-to-late stages of carbonatite evolution. Two varieties of amphibole are reported for the first time from this complex, ferri-winchite and cummingtonite; the former is magmatic and the latter is metamorphic in origin. The columbite–tantalite-series minerals are columbite-(Fe), and their paragenesis evolves from composite grains with pyrochlore to individual crystals. Pyrochlore is magmatic with U–Ta–Ti-rich compositions and shows evolution from calciopyrochlore to kenopyrochlore, followed by alteration during late-stages of carbonatite evolution. Monazite and baryte constitute the post-magmatic mineral assemblage; the former is hydrothermal and crystallised after precursor apatite, whereas the latter is associated exclusively with columbite–pyrochlore composites. On the basis of the mineralogy of the carbonatite, it is concluded that the parent magma was generated by low-degree partial melting of magnesite–phlogopite-bearing peridotite.

The new mineral libbyite (IMA2022-091), (NH4)2(Na2□)[(UO2)2(SO4)3(H2O)]2⋅7H2O, was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as tightly intergrown aggregates of light green–yellow equant crystals in a secondary assemblage with bobcookite, coquimbite, halotrichite, metavoltine, rhomboclase, römerite, tamarugite, voltaite and zincorietveldite. The streak is very pale green yellow and the fluorescence is strong green under 405 nm ultraviolet light. Crystals are transparent with vitreous lustre. The tenacity is brittle, the Mohs hardness is ~2½, the fracture is curved. The mineral is soluble in H2O and has a calculated density of 3.465 g⋅cm–3. The mineral is optically uniaxial (–) with ω = 1.581(2) and ɛ = 1.540(2). Electron microprobe analyses provided (NH4)1.92K0.08Na2.00U4.00S6.00O41H18.00. Libbyite is tetragonal, P41212, a = 10.7037(11), c = 31.824(2) Å, V = 3646.0(8) Å3 and Z = 4. The structural unit is a uranyl–sulfate sheet that has the same topology as the sheets in several synthetic uranyl selenates.

An investigation of 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 a mineral that can be identified as the original stannopalladinite described in 1947. As the literature information on the latter is controversial, the mineral was re-investigated 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 colour 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 per formula unit 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) and 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 and 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.