Heflikite, the first Sc-dominant epidote-supergroup mineral, was discovered in two occurrences. The holotype was found in a granitic pegmatite associated with rodingite-like calc-silicate rocks and metasomatised granitic bodies exposed in a serpentinite quarry at Jordanów Śląski near Sobótka, Lower Silesia, SW Poland. The cotype comes from the Heftetjern pegmatite, Tørdal region, Norway. The holotype is composed of (in wt.%): 35.69 SiO2, 0.22 TiO2, 21.98 Al2O3, 6.12 Sc2O3, 0.07 V2O3, 1.10 Fe2O3, 0.11 Y2O3, 1.55 La2O3, 4.05 Ce2O3, 0.31 Pr2O3, 1.53 Nd2O3, 0.40 Sm2O3, 0.11 EuO, 0.56 Gd2O3, 0.14 MnO, 3.56 FeO, 0.16 MgO, 19.16 CaO and 1.78 H2O(+)calc.; total 98.60. The cotype contains: 34.92 SiO2, 0.44 TiO2, 0.82 SnO2, 19.13 Al2O3, 4.79 Sc2O3, 1.96 Fe2O3, 2.55 La2O3, 7.39 Ce2O3, 0.48 Pr2O3, 0.67 Nd2O3, 0.12 EuO, 0.61 Gd2O3, 0.13 MnO, 5.97 FeO, 17.66 CaO and 1.73 H2O(+)calc.; total 99.37. The compositions correspond to the following empirical formulae: (Ca1.729Ce0.125La0.048Nd0.046Gd0.016Sm0.012Pr0.010Y0.005Eu2+0.003)Σ1.994[(Al2.182Sc0.449Fe3+0.070V3+0.005)Σ2.706(Fe2+0.251Mg0.020Mn0.010)Σ0.281Ti0.014]Σ3.001(Si3.006O11)O(OH) and (Ca1.644Ce0.235La0.082Nd0.021Gd0.018Pr0.015Eu2+0.004)Σ1.019[(Al1.958Sc0.362Fe3+0.128)Σ2.448(Fe2+0.434Mn0.009)Σ0.443(Ti0.029Sn0.029)Σ0.058]Σ2.949(Si3.033O11)O(OH), respectively, and to the ideal formula Ca2(Al2Sc)(Si2O7)(SiO4)O(OH). The crystal structure of the holotype was refined in the monoclinic system with an R1 index of 8.62%. The crystal-structure refinement indicates exclusively Si occupied T sites, Al occupied M1 and M2 sites, and a Ca occupied A1 site. The M3 site is filled predominantly by trivalent cations, mainly Sc3+, with divalent cations (mainly Fe2+) as minor occupants. The A2 site is filled mostly by Ca with minor amounts of rare earth elements (REE). The holotype heflikite crystallised from metasomatic fluids that infiltrated a contact between the granitic pegmatite and the surrounding rodingite-type calc-silicate rocks and serpentinites. The fluids that introduced Sc into the pegmatite could have been either hydrothermal or related to low-grade regional metamorphism that postdated the formation of the pegmatite. The cotype heflikite formed during the late-stage hydrothermal crystallisation of the Sc-enriched granitic pegmatite.

Monazites are one of the most interesting groups of accessory mineral components of crystalline rocks due to the information on geochemical evolution of the crystallisation environment coded in their chemical compositions, in addition to comprising one of the most valuable objects for geochronology studies. This paper presents monazite-(Sm) and monazite-(Nd) from the Blue Beryl Dyke of the Julianna system of rare-element pegmatites at Piława Górna, Lower Silesia, Poland. These monazites are unique due to their unusually high Sm and Nd contents, reaching 33.22 wt.% Sm2O3 and 34.12 wt.% Nd2O3, respectively. We consider the most significant factors of the enrichment in Sm and Nd to be the occurrence of highly fractionated pegmatite-forming melts during the final stages of solidification and associated hydrothermal fluids that were strongly enriched in rare earth element REE–Cl and REE–F complexes. Local disequilibria allowed for the rapid growth of accessory phases under supercooling conditions associated with the scavenging of selected elements, leading to their local depletion, which was not balanced by diffusion processes. As a consequence, the depletion of light rare earth elements (LREE) led to the incorporation of available middle rare earth elements (MREE, Sm–Dy) in the case of Sm and Nd, which could occupy an acceptable structural position in minerals of the monazite group.

Two silesiaite crystals, one from Szklarska Poręba, Poland (type locality), and the other from Häiviäntien, Finland, were studied with electron-probe microanalysis, Raman spectroscopy and single-crystal X-ray diffraction. The crystals have the following compositions normalised to 13 O2– + 1 (OH)– anions: Ca2.001(2)[(Sn1.105(6)Zr0.009(1))Σ1.114(Fe3+0.523(78)Sc0.185(62)Al0.070(14))Σ0.779(Fe2+0.065(12)Mn2+0.041(5)Mg0.003(3))Σ0.110]Σ2.003(Si3.997(2)O13OH), and Ca2.006(8)[(Sn1.110(18)Ti0.006(3))Σ1.107(Fe3+0.648(50)Al0.063(11))Σ0.710(Fe2+0.140(30)Mn2+0.011(3)Mg0.005(2))Σ0.155(Nb0.020(6)Ta0.011(3))Σ0.040]Σ2.009(Si3.991(14)O13OH), respectively. The structure of the crystals was refined in the triclinic system with unconventional space-group symmetry C1 to R1 = 2.02% and 3.56%, respectively. The unit cells were found to be a = 10.0080(2), b = 8.3622(1), c = 13.2994(2) Å, α = 89.987(1), β = 109.095(2), γ = 89.978(1)° and V = 1051.77(3) Å3 for silesiaite from Szklarska Poręba, and a = 9.9985(3), b = 8.3446(2), c = 13.2760(4) Å, α = 89.986(3), β = 109.122(2), γ = 90.020(2)° and V = 1046.55(5) Å3 for silesiaite from Häiviäntien. In both crystals, the Ca sites are occupied solely by calcium and Si sites by silicon atoms. Optimised occupancies of the four M sites indicated slightly different site fillings. In the Szklarska Poręba silesiaite, the M1 site is predominantly occupied by trivalent Fe + Sc and the M2–M4 sites by Sn. In contrast, in the Häiviäntien silesiaite, the M1–M3 sites are Sn-dominant, while Fe3+ predominantly occupies the M4 site. The differences can be considered a result of an evolution of the M1–M4 site occupancies following a decrease of the <M–O> distance. Among the minerals of the kristiansenite group, Sc-free silesiaite from the Häiviäntien pegmatite has the smallest average radius of M-site cations and a unit-cell volume that increases proportionally to the (Fe2+ ± Sc) content. The hydrogen atoms form moderate hydrogen bonds between disilicate groups (Si2O7 and Si2O6OH) linked in rows along [101], indicating the presence of one hydroxyl in the formula calculated for Z = 4. All three kristiansenite-group species, i.e. silesiaite, kozłowskiite and kristiansenite, are isostructural.

Two tourmaline samples occurring in quartz veinlets, which cross-cut an amphibolite body at the Budniki camp near the Kowary town in the south-west part of the Karkonosze Mountains, SW Poland, were studied through microprobe and single crystal X-ray diffraction. Samples were extracted from core and rim regions of crystals with concentric zoning. Chemical and structural data revealed that the core tourmaline is characterised by a dravite–oxy-dravite composition, with the formula: X(Na0.82Ca0.07K0.01Sr0.01□0.09)Σ1Y(Mg1.73Fe2+0.81Fe3+0.41Ti0.04V0.01)Σ3Z(Al5.85Fe3+0.15)Σ6(TSi6O18)(BO3)3(OH)3W(OH0.50O0.50)Σ1 and unit cell parameters a = 15.97377(14) Å and c = 7.22644(7) Å. The rim part of the crystals has a magnesio-lucchesiite composition, described by the formula: X(Ca0.49Na0.41K0.04Sr0.02□0.04)Σ1Y(Mg1.87Fe2+0.95Ti0.15Fe3+0.02V0.02)Σ3Z(Al5.49Fe3+0.51)Σ6(BO3)3(TSi6O18)(OH)3W(O0.81F0.18OH0.01)Σ1 with unit cell parameters a = 15.9863(3) Å and c = 7.22426(15) Å. Both tourmalines show similar refined populations at the Y and Z sites: Y[(Fe2+0.810Mg0.680)Σ1.490(Al1.044Fe3+0.413V0.009)Σ1.465Ti0.045]Σ3Z(Al4.806Mg1.042Fe3+0.152)Σ6 (dravite–oxy-dravite), and Y[(Fe2+0.945Mg0.750)Σ1.695(Al0.737Fe3+0.404V0.018)Σ1.159Ti0.146]Σ3Z(Al4.749Mg1.115Fe3+0.137)Σ6 (magnesio-lucchesiite), with a comparable Mg/(Mg + Fe) ratio of ~0.54–0.56, oxidation of Fe expressed as Fe3+/Fetotal ratio ~0.36–0.41, and trace components such as Ti, Sr, V, Cr, Ni and Co. The geological history of the eastern Karkonosze region in the Kowary vicinity indicates that both tourmalines crystallised from B-bearing metamorphic fluids mobilised by Variscan prograde metamorphism from the protoliths of the Velká Upá mica schists that host the Budniki amphibolite. The fluids migrated into the tectonised amphibolite enriched in Ti, V, Cr, Ni and Co, and mineralised the fractures within it through deposition of soluble species in the form of quartz–tourmaline veinlets. Magnesio-lucchesiite crystallised in an early retrogression stage, probably from Ca- and F-bearing fluids secondary enriched in B by the dissolution of dravite–oxy-dravite. The Budniki camp is, in addition to the type and co-type magnesio-lucchesiite localities, the third documented occurrence of the species worldwide.

Kozłowskiite, ideally Ca4(Fe2+Sn3)(Si2O7)2(Si2O6OH)2, is a new mineral isostructural with kristiansenite and silesiaite, found as a band in the core of a zoned silesiaite–kristiansenite crystal from the granitic pegmatite at Szklarska Poręba, Lower Silesia, Poland. In tiny pieces kozłowskiite is pale brownish, with a calculated density of 3.775 g⋅cm–3 and a mean refractive index ~1.727. The triclinic crystal structure was determined with space-group symmetry C1: a = 10.0183(2), b = 8.3861(1), c = 13.3395(2) Å, α = 89.956(1), β = 109.039(2), γ = 89.979(1)° and V = 1059.40(3) Å3, although, similarly to kristiansenite, it is metrically monoclinic (Laue group 2/m) with α and γ angles equal to 90° and a = 10.0170(3), b = 8.3860(2), c = 13.3421(4) Å, β = 109.050(3)° and V = 1059.40(5) Å3. The seven strongest reflections in the calculated powder X-ray diffraction pattern are [d in Å (I) hkl]: 5.190 (73.2) 111, 1$\bar{1}$1; 4.569 (30.0) $\bar{2}$02; 3.153 (64.7) 004; 3.094 (28.1) $\bar{3}$11, $\bar{3}\bar{1}$1; 3.089 (100) $\bar{2}\bar{2}$2, $\bar{2}$22; 2.595 (27.2) 2$\bar{2}$2, 222; and 2.141 (30.6) $\bar{3}$31, $\bar{3}\bar{3}$1. Electron microprobe analysis gave (in wt.%) SiO2 39.46, ZrO2 0.35, SnO2 31.13, Al2O3 0.35, Sc2O3 2.65, total Fe as Fe2O3 5.06 (= Fe2O3calc. 2.26; FeOcalc. 2.52), MnO 0.71, CaO 18.42 and H2Ocalc. 1.48, sum 99.33. The empirical formula on the basis of 26O + 2(OH) and 16 cations (Z = 2) is Ca4.00(Sn2.52Sc0.47Fe2+0.43Fe3+0.34Mn2+0.12Al0.08Zr0.03)Σ4.00(Si2.00O7)2(Si2.00O6OH)2. The crystal structure of kozłowskiite was refined to an R1 = 2.12% for 4887 reflections with Io>2σI. The Ca and Si sites are occupied solely by Ca and Si, respectively, and three of four M sites: M2, M3 and M4, are dominated by Sn. Four hydrogen atoms present in the kozłowskiite unit cell are shared among the O17–O27 and O47–O37 oxygen atoms where O17 and O47 are OH groups forming relatively strong hydrogen bonds.

Beusite-(Ca), ideally Ca${\rm Mn}_{\rm 2}^{2 +} $(PO4)2, is a new graftonite-group mineral from the Yellowknife pegmatite field, Northwest Territories, Canada. It occurs in a beryl–columbite–phosphate rare-element pegmatite where it is commonly intergrown with triphylite–lithiophilite or sarcopside, and may form by exsolution from a high-temperature (Li,Ca)-rich graftonite-like parent phase. It occurs as pale-brown lamellae 0.1–1.5 mm wide in triphylite, and is pale brown with a vitreous lustre and a very pale-brown streak. It is brittle, has a Mohs hardness of 5, and the calculated density is 3.610 g/cm3. Beusite-(Ca) is colourless in plane-polarized light, and is biaxial (+) with α = 1.685(2), β = 1.688(2), γ = 1.700(5), and the optic axial angle is 46.0(5)°. It is non-pleochroic with X || b; Y ˄ a = 40.3° in β obtuse; Z ˄ a = 49.7° in β acute. Beusite-(Ca) is monoclinic, has space group P21/c, a = 8.799(2), b = 11.724(2), c = 6.170(1) Å, β = 99.23(3)°, V = 628.3(1) Å3 and Z = 4. Chemical analysis by electron microprobe gave P2O5 41.63, FeO 19.43, MnO 23.63, CaO 15.45, sum 100.14 wt.%. The empirical formula was normalized on the basis of 8 anions pfu: (Ca0.94Fe0.92Mn1.13)Σ2.99(PO4)2.00. The crystal structure was refined to an R1 index of 1.55%. Beusite-(Ca) is a member of the graftonite group with Ca completely ordered at the [8]-coordinated M(1) site.

A classification and nomenclature scheme has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification for the minerals of the graftonite group. The crystal structures of these minerals have three distinct sites that are occupied by Fe2+, Mn2+ and Ca2+. These sites have coordination numbers [8], [5] and [6], and these differences lead to very strong order of Fe2+, Mn2+ and Ca2+ over these sites. As a result of this strong order, the following compositions have been identified as distinct species: graftonite: FeFe2(PO4)2; graftonite-(Ca): CaFe2(PO4)2; graftonite-(Mn): MnFe2(PO4)2; beusite: MnMn2(PO4)2; and beusite-(Ca): CaMn2(PO4)2.

Two new minerals of the graftonite group, graftonite-(Mn), ideally M(1)MnM(2),M(3)Fe2(PO4)2, and graftonite-(Ca), ideally M(1)CaM(2),M(3)Fe2(PO4)2, were discovered in phosphate nodules of two beryl–columbite–phosphate pegmatites at Lutomia and Michałkowa, respectively, in the Góry Sowie Block, Lower Silesia, southwest Poland. Graftonite-(Mn) is pinkish brown, whereas graftonite-(Ca) shows more brownish colouration. Both minerals have a vitreous lustre, a good cleavage observed along (010) and irregular fracture; both are transparent and neither of them is fluorescent. They are brittle and have a Mohs hardness of ~5. The minerals are non-pleochroic, colourless in all orientations, biaxial (+), with mean refractive indices α = 1.710(2) and 1.690(2), β = 1.713(2) and 1.692(2), and γ = 1.725(2) and 1.710(5), respectively. With complete order of Ca at the M(1) site, the formulae of the holotype crystals are M(1)(Mn0.70Ca0.30)M(2),M(3)(Fe1.34Mn0.60Mg0.06Zn0.01)Σ3(PO4)2 for graftonite-(Mn) and M(1)(Ca0.98Mn0.02)M(2),M(3)(Fe1.38Mn0.56Mg0.05)Σ3(PO4)2 for graftonite-(Ca). Both crystal chemistry and crystal-structure refinement (R1 = 2.34 and 1.63%, respectively) indicate that the M(1) site is occupied dominantly by Mn in graftonite-(Mn) and by Ca in graftonite-(Ca), and the M(2) and M(3) sites are occupied by Fe2+ and Mn2+, with Fe2+ dominant over Mn2+ at the aggregate M(2) + M(3) sites. Graftonite-(Mn) and graftonite-(Ca) are isostructural with graftonite, M(1)FeM(2),M(3)Fe2(PO4)2 (monoclinic system; space-group symmetry P21/c), with the unit-cell parameters a = 8.811(2) Å, b = 11.494(2) Å, c = 6.138(1) Å, β = 99.23(3)° and V = 613.5(4) Å3, and a = 8.792(2) Å, b = 11.743(2) Å, c = 6.169(1) Å, β = 99.35(3)° and V = 628.5(1) Å3, respectively. The densities calculated on the basis of molar weights and unit-cell volumes are 3.793 g/cm3 for graftonite-(Mn) and 3.592 g/cm3 for graftonite-(Ca). The eight strongest lines in powder X-ray diffraction patterns on the basis of single-crystal data are, respectively [d, Å, I (hkl)]: 2.874, 100, (230 + 040); 2.858, 79, (221); 3.506, 73, (130); 2.717, 79, ($\bar{3}$11); 2.952, 55, (131); 2.916, 53, ($\bar{1}$12); 2.899, 44, (300); 3.016, 35, ($\bar{1}$02); and 3.654, 100, (130); 2.979, 85, (221); 3.014, 77, (230); 3.042, 76, (040 + $\bar{1}$12); 2.834, 68, ($\bar{3}$11); 3.097, 57, (131); 3.133, 56, ($\bar{1}$02); 2.542, 30, (311). Both minerals are common primary phosphates in phosphate nodules, occurring as lamellar intergrowths with sarcopside ± triphylite/lithiophilite, products of exsolution from a (Li,Ca)-rich graftonite-like parent phase crystallized at high temperature from P-bearing hydrosaline melts.

Yellowish dravitic tourmaline (dominated by the oxy-dravite component) associated with secondary fluor-dravite/fluor-schorl and dravite/schorl tourmalines was found in a quartz vein cropping out in the eastern part of the Karkonosze Mountains range, SW Poland. The crystal structure of this tourmaline was refined to an R1 value of 1.85% based on single-crystal data, and the chemical composition was determined by electron-microprobe analysis. The tourmaline, a representative of the alkali-tourmaline group, has the structural formula: (Na0.75Ca0.12□0.13)Σ1(Mg1.93Al0.95Ti0.06${\rm Fe}_{{\rm 0}{\rm. 04}}^{{\rm 2 +}} $ V0.01)Σ3(Al5.38Mg0.62)Σ6B3Si6O27(OH)3(O0.46OH0.33F0.21)Σ1, and is characterized by an extremely high Mg/(Mg + Fe) ratio of 0.97–0.99, the WO2– content that reaches 0.59 apfu resulting in a local predominance of the oxy-dravitic component and Mg–Al disorder on the octahedral Y and Z sites of the order of 0.64 apfu. This disordering results in an increasing <Z–O> distance with ~1.925 Å, and unit-cell parameters a = 15.916(1) Å and c = 7.180(1) Å. The tourmaline formed during Variscan prograde metamorphism under the influence of a released (H2O,B,F)-bearing fluid. The fluid mobilized the most soluble components of partly altered silicic volcaniclastic material of the Late Cambrian to Early Ordovician bimodal volcanism to become the protolith for adjacent quartzo-feldspathic schists and amphibolites, and propagated them into the surrounding granitic gneisses of the Kowary unit in the eastern metamorphic cover of the Karkonosze granite.

Maneckiite, ideally NaCa2Fe22þ (Fe3+Mg)Mn2(PO4)6(H2O)2, was found in a pegmatite at Michałkowa, Góry Sowie Block, SW Poland. The mineral forms subhedral and anhedral crystals ~150 μm × 150 μm in the outer zone of phosphate nodules, where it is associated with fluorapatite, wolfeite, Ca-rich graftonite and alluaudite-group minerals. Maneckiite is transparent, dark brown, with a colourless streak and vitreous lustre, brittle, and has a good cleavage // {010}, a splintery fracture and a Mohs hardness of ~5. The calculated density is 3.531 g cm–3. Maneckiite is pleochroic: α = dark green, β = dark blue/green, γ = light brown/tan, biaxial (+) with refractive indices α = 1.698(2), β = 1.706(2), γ = 1.727(2) and birefringence Δ = ~0.03; 2Vmeas. = 65.9 (1.5)° and 2Vcalc. = 64°, dispersion is obscured by the dark colour, and optical orientation X//a, Y//b, Z//c. Maneckite is orthorhombic (Pcab) and has unit-cell parameters a = 12.526(4) Å, b = 12.914(5) Å, c = 11.664(4) Å and V = 1886.8(5) Å3. The strongest reflections are (dhkl in Å; I; hkl): 2.759, 100, 402; 2.916, 78, 004; 3.020, 68, 401; 2.844, 35, 014; 2.869, 31, 240; 2.825, 30, 042. Maneckiite has the wicksite structure and is its M(3)Mn-analogue. The mineral crystallized as a product of Na- and Ca-metasomatism induced by a HT fluid in the presence of Al3+ from a neighbouring aluminosilicate melt. A Gladstone-Dale index, 0.027, places maneckiite in the category ‘excellent’.

Pilawite-(Y), ideally Ca2(Y,Yb)2Al4(SiO4)4O2(OH)2, was discovered in a pegmatite near Piława Górna, Lower Silesia, Poland. The mineral occurs as white, translucent, brittle crystals up to 1.5 mm in size. It has a white streak, vitreous lustre and a hardness of 5 on Mohs scale. The calculated density is 4.007 g/cm3. Pilawite-(Y) is non-pleochroic, biaxial (+), with refractive indices α = 1.743(5), β = 1.754(5) and γ = 1.779(5), birefringence Δ = 0.03–0.04, 2Vmeas. = 65(2)° and 2Vcalc. = 68°. Pilawite-(Y) is monoclinic P21/c, with unit-cell parameters a = 8.558(3) Å, b = 7.260(3) Å, c = 11.182(6) Å, β = 90.61(4)o, V = 694.7(4) Å3. The crystal structure was refined to an R1 index of 2.76% and consists of chains of edge- and corner-sharing octahedra decorated by tetrahedra and having the stoichiometry [Al2(SiO4)4O(OH)] that link by sharing corners to form an octahedron–tetrahedron framework with large interstices that contain Ca2+ and (Y,Ln)3+. It is a graphical isomer of the Al–P framework in palermoite, Sr2Li4[Al2(PO4)2(OH)2]2. The pilawite-(Y)-bearing assemblage began crystallization at high Y + Ln activities and was modified progressively by a Ca-enriched fluid, resulting in the sequence: keiviite-(Y) → gadolinite-(Y) to hingganite-(Y) + hellandite-(Y) → pilawite-(Y) → allanite-(Y) → epidote/zoisite.

Motukoreaite, Mg6Al3(OH)18[Na(H2O)6][SO4]2·6H2O, is a poorly-known, rare layered double hydroxide mineral belonging to the wermlandite group in the hydrotalcite supergroup. It was found in abundant quantities (at least hundreds of thousands of Mt) in the roof part the Younger Potash unit of the Leine cyclothem on the Kłodawa Salt Dome in central Poland (Permian–Mesozoic basin of Central Europe), outside its known typical environments like altered basalts and basaltic tuffs, including those deposited in submarine volcanic areas. The mineral displays varying SO2–4, Na+ and H2O contents with negligible CO2–3, corresponding to the mean composition Mg5.75(Al3.20Fe3+0.04)∑3.25(OH)18.00{[Na(H2O)6]0.72□0.28}[(SO4)1.67(CO3)3.03(OH)0.57]·0.72H2O. It can be related to the partly dehydrated, hypothetical end-member Mg6Al3(OH)18[Na(H2O)6][(SO4)2]·6H2O. The Kł odawa motukoreaite represents the hexagonal, 3-layer polytype with the 3 × 3 superstructure in the xy plane, and unit cell a = b = 9.191(2)–9.199(2) Å, i.e. = 3 × 3.064–3.066 Å and c = 33.529(9)–33.562(7) Å, i.e. = 3 × 11.174–11.187 Å. The mineral was formed by alteration of clays delivered to the basin by an aeolian overprint and co-sedimented along with the evaporite sequence, initiated under the influence of Mg2+ - and SO2–4-bearing brines at temperatures not exceeding 160–200°C, released from the evaporites during diagenetic/metamorphic processes.

Żabińskiite, ideally Ca(Al0.5Ta0.5)(SiO4)O, was found in a Variscan granitic pegmatite at Piława Górna, Lower Silesia, SW Poland. The mineral occurs along with (Al,Ta,Nb)- and (Al,F)-bearing titanites, a pyrochlore-supergroupmineral and a K-mica in compositionally inhomogeneous aggregates, ∼120 μm × 70 μm in size, in a fractured crystal of zircon intergrown with polycrase-(Y) and euxenite-(Y). Żabińskiite is transparent, brittle, brownish, with a white streak, vitreous lustre and a Mohs hardness of ∼5. The calculated density for the refined crystal is equal to 3.897 g cm–3, but depends strongly on composition. The mineral is non-pleochroic, biaxial (–), with mean refractive indices ≥1.89. The (Al,Ta,Nb)-richest żabińskiite crystal,(Ca0.980Na0.015)∑=0.995(Al0.340Fe3+0.029Ti0.298V0.001Zr0.001Sn0.005Ta0.251Nb0.081)∑=1.005[(Si0.988Al0.012)O4.946F0.047(OH)0.007)∑=5.000];60.7 mol.% Ca[Al0.5(Ta,Nb)0.5](SiO4)O; is close in composition to previously described synthetic material. Żabińskiite is triclinic (space group symmetry A1) and has unit-cell parameters a = 7.031(2) Å, b = 8.692(2) Å,c = 6.561(2) Å, α = 89.712(11)°, β = 113.830(13)°, γ = 90.352(12)° and V = 366.77 (11) Å3. It is isostructural with triclinic titanite and bond-topologically identical with titanite and other minerals of the titanite group.Żabińskiite crystallized along with (Al,Ta,Nb)-bearing titanites at increasing Ti and Nb, and decreasing Ta activities, almost coevally with polycrase-(Y) and euxenite-(Y) from Ca-contaminated fluxed melts or early hydrothermal fluids.