The new mineral leishmanite (IMA2026-002), Ba(H2O)4[(UO2)3O2(OH)3]2·3H2O, was found in the small uranium occurrence near Nendaz, Valais, Switzerland, where it occurs as elongated tabular crystals (up to 0.1 mm) in a peculiar assemblage with parauranophane and ‘biotite’ in a thin quartz veinlet, concordant with the schistosity of a very finely bedded paragneiss; the origin of the mineral is most probably from the retrograde metamorphic fluids. The streak is pale yellow. Crystals are translucent with vitreous lustre. The tenacity is brittle, the Mohs hardness is ∼2½, and the fracture is curved. The mineral has Dcalc. of 5.217 g·cm–3 for the ideal formula. The mineral is optically biaxial (–) with α = 1.755(3), β = 1.796(3) and γ = 1.799(3); 2V is 28(2)°; orientation is X = b, Y and Z lie in {010}; pleochroism: X colourless, Y yellow, Z yellow; X < < Y < Z. Electron microprobe analyses provided (Ba0.91Pb0.07K0.06)Σ1.04(H2O)4[(UO2)6O4.02(OH)5.98]·3H2O. Leishmanite is orthorhombic, Pmn21, a = 12.079(2), b = 15.096(3), c = 7.155(2) Å, V = 1304.7(5) Å3 and Z = 2. The crystal structure (R1 = 0.0392 for 6324 I > 3σI reflections) contains uranyl-oxo-hydroxo sheets of both the α-U3O8 (protasite) topology with the PD stacking sequence and β-U3O8 topology with the DRU stacking sequence. Between the sheets, Ba2+ is coordinated by three H2O molecules, and an additional four H2O molecules are not bonded to any metal cation. The structure and chemical composition of leishmanite are discussed with respect to the paragenetic relationships within alteration associations of uraninite, based on the bond-valence approach.

In the extreme thallium (Tl) environments, such as oxidation zones of Tl-bearing sulfide deposits including mining wastes and technosols, Tl is retained mostly through formation of secondary Tl minerals or Tl-adsorption onto micaceous phyllosilicates and illite-like clay minerals. To better understand Tl-retention processes and phase formation in such environments we have synthesized high-quality single crystals of three mineral-like Tl salts using hydrothermal methods. These are thallium(I) triiron(III) bis(sulfate) hexahydroxide doped by small amounts of K+ and Al3+, (Tl0.91K0.09)(Fe2.90Al0.10)(SO4)2(OH)6 (I), aluminium thallium bis(sulfate) dodecahydrate Tl+Al(SO4)2·12H2O (II) and ferric iron thallium bis(sulfate) Tl+Fe3+(SO4)2 (III). They were characterized through single-crystal X-ray diffraction (SCXRD), Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) and partly by transmission electron microscopy (TEM). The compounds I and III crystallise in trigonal centrosymmetric space groups: I in R$\overline 3 $m with a = 7.3330(4), c = 17.7118(6) Å and III in R$\overline 3 $ with a = 4.8375(2), c = 24.7905(9) Å, whereas II is cubic, space group Pa$\overline 3 $, with a = 12.2727(14) Å. I and II, are synthetic analogues of the minerals dorallcharite and lanmuchangite, respectively. Synthetic dorallcharite (I) is isostructural with minerals in the jarosite–alunite series, KFe3+3(SO4)2(OH)6–KAl3(SO4)2(OH)6, while synthetic lanmuchangite (II), nominally TlAl(SO4)2·12H2O, is a cubic thallium alum, a type of hydrated double sulfate salt isostructural with the β-alum, CsAl(SO4)2·12H2O. The crystal structure of III, TlFe3+(SO4)2, is like that of the mineral steklite, KAl(SO4)2. II and III chemically belong to the group of alums with different degrees of hydration. The O–H···O hydrogen bonds in I and II assemble water molecule H2O and hydroxide OH– ions into several various hydrogen bond networks. The structural connections to the related minerals and inorganic compounds of I–III have been discussed. Our findings provide new insights into the chemical and structural properties of dorallcharite and lanmuchangite, enhancing our understanding of their formation in Nature. The findings also suggest the potential natural occurrence of TlFe(SO4)2, offering valuable implications for the role of sulfates in the environmental cycling of Tl.

The new mineral, babunaite-(Nd) NdAsO4, was discovered in metasomatic rocks of the Mixed Series near the Nežilovo village in Northern Macedonia. These rocks are characterised by an unusual occurrence of Pb-Zn oxide ore mineralisation. This area forms part of the high-grade metamorphic region of the Upper Precambrian Pelagonian massif. Babunaite-(Nd) is an accessory mineral in pink schists, which mainly consists of Mn-bearing muscovite and quartz, with minor braunite. Accessory minerals are hematite, gahnite, almeidaite, långbanite, zircon, piemontite and piemontite-(Pb), nežilovite, Sb-bearing rutile, fluorapatite, As-bearing fluorapatite, gasparite-(La), chernovite-(Y), arsenoflorencite-(La). Babunaite-(Nd) forms single crystals measuring up to 70 μm in size. The transparent crystals exhibit an adamantine lustre and a pale-yellow colour. The microhardness of babunaite-(Nd) is VHN25 = 578(21) kg/mm2, equivalent to a hardness of 5 on the Mohs scale. The mineral is brittle and does not exhibit cleavage. The mean composition of the holotype crystal is as follows: (Nd3+0.39Ca0.14Th0.09Pr3+0.08La0.07Sm3+0.06Y0.06Gd0.05Ce3+0.02Eu3+0.01)Σ0.97(As5+0.95W6+0.05V5+0.01)Σ1.02O4. The calculated density is 5.918 g·cm–3. Babunaite-(Nd), with the general crystal chemical formula ABO4, has a scheelite-type structure and crystallises in the tetragonal I41/a space group: a = 5.1363(2) Å, c = 11.5764(8) Å, V = 305.41(3) Å3 and Z = 4. The main bands at 190, 348, 440 and 833 cm–1 are distinguished in the Raman spectrum of babunaite-(Nd). A synthetic analogue of babunaite-(Nd) is known, which forms under high-pressure and high-temperature conditions of 11 GPa and 1100–1300°C. The genesis of the Mixed Series rocks occurred under metamorphic conditions approaching the parameters of the kyanite–graphite subfacies, at which gasparite-(Nd) with the monazite structure should form. The formation of babunaite-(Nd) is associated with the stabilisation of its structure by a tungsten (W) impurity. It is the first arsenate phase containing rare earth elements (REE) in the scheelite group.

New crystallographic data are reported for pseudojohannite, Cu3(OH)2[(UO2)4O4(SO4)2](H2O)12, from the type locality Jáchymov, Czech Republic. The structure refinement is based on a dataset collected with high redundancy (8.62) using a brilliant X-ray microfocus source, which provided sufficient quality to localize hydrogen atoms from difference-Fourier maps. The pseudojohannite crystal studied is triclinic at 100 K, with the space group P$\overline 1 $, with a = 8.6697(4), b = 8.8712(5), c = 9.9825(6) Å, α = 71.775(6)°, β = 70.663(5)°, γ = 76.011(5)°, with V = 679.88(7) Å3 and Z = 1. The final refinement converged to R1 = 0.0198 for 6029 unique reflections with I > 3σ(I) and wR2 = 0.0699 for all 6924 reflections. The bond-valence analysis for the structure and the determined positions of H atoms provided complete information on the nature of bonding between the [(UO2)4O4(SO4)2] structural units and the interlayer complex in pseudojohannite. In total, there are eight transformer H2O groups, four non-transformer H2O (two of which are not directly linked to any metal cation sites), and two OH– groups. The structure formula of pseudojohannite can be written as Cu3(H2[3]O)8(H2[4]O)2(OH)2[(UO2)4O4(SO4)2](H2[4]O)2 (Z = 1). Pseudojohannite represents a well-ordered triclinic zippeite-type structure.

Hydrocalumite, a natural Ca-Al Layered Double Hydroxide (LDH), also known as a hydrated calcium aluminate and an aluminate ferrite monosubstituted (AFm) phase in cement chemistry, has been studied by single-crystal and powder X-ray diffraction, electron probe microanalysis and Raman spectroscopy on a sample from Boisséjour, Puy-de-Dôme, Auvergne-Rhône-Alpes, France. The mineral is monoclinic, space group P2/c, a = 10.0234(3), b = 11.5131(3), c = 16.2989(5) Å, β = 104.205(3)°, V = 1823.39(9) Å3 and Z = 4. The crystal structure has been refined to R1 = 0.0505 based on 6296 unique reflections. The empirical chemical formula of the mineral (Ca, Al, Cl according to electron probe microanalysis; CO2, OH and H2O on the basis of crystal-structure refinement and Raman spectroscopy) is Ca3.96Al2.04(OH)12.04Cl0.96(CO3)0.5˙5H2O that can be idealized as Ca4Al2(OH)12Cl(CO3)0.5·5H2O. The presence of (CO3)2– and (OH)– anionic groups and (H2O)0 molecules is confirmed by Raman spectroscopy. The strongest reflections in the powder X-ray diffraction pattern are (d in Å, Irel in %): 7.89, 100; 3.951, 34; 3.860, 59; 3.753, 26; 2.884, 73; 2.527, 27; 2.501, 38; 2.453, 64; 2.433, 30; 2.327, 25. The crystal structure study reveals the ordering of interlayer species: Cl– and (CO3)2– anions and H2O molecules, which means that both anions play a species-defining role in contrast to the previous suggestions on mono-anionic end-members (with either Cl or OH or CO3 anions). The ordering of two different anions is usually not observed for other LDHs and appears to be a crystal-chemical feature of the Ca-Al LDH members. This work is dedicated to the 150th anniversary of the Mineralogical Society of the UK and Ireland. Hydrocalumite is a mineral with a 90-year history starting from North Ireland, UK, and is a good example of joint efforts of different mineralogical scientific societies in deciphering scientific puzzles.

The new mineral almagreraite (IMA2025-025), Cu2+ZnMn4+3O8, was found on the dump of the República Romana mine, Sierra Almagrera, Cuevas del Almanzora, Almería, Andalusia, Spain, where it occurs as tapering prisms or blades up to ∼0.4 mm in length, commonly forming subparallel to divergent aggregates. It is a secondary mineral associated intimately with well-crystallized blades of malachite on a matrix consisting of well-crystallized goethite and massive friable hematite. Crystals are black and opaque with submetallic lustre. The streak is dark grey with a brownish tint. The tenacity is brittle and the fracture is splintery. There are probably two cleavages (possibly {100} and {010}). The Mohs hardness is ∼5. The calculated density is 5.174 g·cm–3 based upon the empirical formula. In reflected light, the mineral is bluish grey in colour with moderate bireflectance and slightly bluish grey to a lighter bluish grey pleochroism. Electron probe microanalyses provided (Mn4+3.05Cu2+0.93Zn0.91Al0.05)Σ4.94O8. Almagreraite is orthorhombic, Pmn21, a = 5.7298(4), b = 4.9715(4), c = 9.3479(7) Å, V = 266.28(3) Å3 and Z = 2. In the crystal structure (R1 = 0.0297 for 423 I > 2σI reflections), Mn4+O6 octahedra share edges forming an octahedral sheet parallel to {001}. One in every four octahedra in the sheet is vacant, providing the sheet formula [Mn4+3O8]4–. Successive sheets are connected via bonds to Cu2+ and Zn2+ located in a layer between the sheets. The structure is similar to that of minerals of the nolanite supergroup and most notably the kamiokite group. Almagreraite is a member of a family of mixed-metal oxides with the generic formula M2Mn3O8, which are an important subject of study for the development of new materials.

The crystal structure of resmetirom heminonahydrate Form CSI has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Form CSI had been described previously as a dihydrate. Resmetirom heminonahydrate Form CSI crystallizes in space group P-1 (#2) with a = 11.3094(23), b = 15.158(6), c = 16.570(7) Å, α = 67.405(13), β = 74.425(7), γ = 69.526(7)°, V = 2,427.2(4) Å3, and Z = 4 at 298 K. The crystal structure consists of layers of resmetirom molecules parallel to the bc-plane. These layers are separated by water-rich layers also parallel to the bc-plane. A strong N–H···O links the two resmetirom molecules. The equivalent amino group in the other molecule acts as a donor to a water molecule. A number of C–H···O and C–H···N hydrogen bonds also contribute to the lattice energy. Water molecules act as donors to both O and N in the resmetirom molecules. The structure is more complicated than a hydrogen-bonded framework of resmetirom molecules with water in the pores. The powder pattern has been submitted to the International Centre for Diffraction Data (ICDD) for inclusion in the Powder Diffraction File™ (PDF®).

The crystal structure of fluvoxamine hydrogen maleate has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Fluvoxamine maleate crystallizes in space group P21/c (#14) with a = 21.6310(15), b = 5.3180(4), c = 19.5555(15) Å, β = 99.979(5)°, V = 2,215.48(25) Å3, and Z = 4 at 298 K. The crystal structure consists of alternating double layers of cations and anions parallel to the bc-plane. Hydrogen bonds link the layers of anions and cations parallel to the bc-plane. The powder pattern has been submitted to the International Centre for Diffraction Data for inclusion in the Powder Diffraction File™ (PDF®).

Arzamastsevite (IMA2024-085), ideally K6Al5Si6O20(OH)4Cl, is a new zeolite with a unique Si(OH)4 group. The mineral was found in natrolitized sodalite syenite from Parguaiv Mt. (67°47′22.4″ N, 34°35′10″ E), Lovozero alkaline massif, Kola Peninsula, Russia. It occurs as short-prismatic crystals (average 60 µm across) and anhedral grains (average 50 µm across) and is associated with alkali feldspar, sodalite, natrolite, aegirine, magnesio-arfvedsonite, loparite, rhabdophane-(Ce), lamprophyllite, sphalerite, galena, pyrrhotite and pyrite. The largest observed arzamastsevite crystal is 180 µm across. Aggregates of 2–5 crystals are typically observed. Arzamastsevite is colourless, with a vitreous lustre and white streak. The mineral is brittle. Cleavage was not observed; the fracture is uneven. The measured density is 2.50(5) g⋅cm–3, the density calculated using the empirical formula and single-crystal unit-cell parameters is 2.51 g⋅cm–3. Arzamastsevite is optically uniaxial (+), ω = 1.530(2), ε = 1.532(2) (589 nm). Chemical data (electron microprobe, wt.%) are: SiO2 37.17, Al2O3 25.98, Fe2O3 0.05, K2O 28.88, Na2O 0.27, Cl 3.54, H2O (calculated from the crystal structure information, i.e. H = 4) 3.71, O=Cl2 –0.80, total 98.80. The empirical formula calculated on the basis of [20 O + 4 (OH)] = –44 apfu is (K5.96Na0.08)Σ6.04[Al4.95Fe3+0.01Si5.01O20]Cl0.97·[Si(OH)4]. Arzamastsevite is tetragonal, space group: I$\overline 4 $2m, with a = 9.8280(5) Å, c = 13.1342(13) Å, V = 1268.63(18) Å3 and Z = 2. The crystal structure was determined from single-crystal data and refined to R1 = 0.08. The crystal structure of arzamastsevite is characterized by the EDI type zeolite tetrahedral framework. The crystal structure of arzamastsevite is generally similar to the crystal structure of kalborsite, but differs in the substitution of the negatively charged [B(OH)4]–-tetrahedra by the neutral [Si(OH)4]0-tetrahedra, which is controlled by the Si:Al ratio of 1:1 within the framework. The strongest lines of the powder X-ray diffraction pattern [d in Å (I) (hkl)] are: 3.4782 (35) (220); 3.2857 (26) (004); 3.1103 (44) (310); 3.0750 (100) (222); 2.9708 (84) (114); 2.8132 (73) (312); and 2.7321 (28) (204). The mineral is named in honour of Dr. Andrey A. Arzamastsev (b. 1950), a prominent Russian geologist and an expert in the petrology of alkaline rocks.

Marinaite, ideally Cu2Fe3+O2(BO3), a new mineral, was found in a high-temperature (400–600°C) crack on the cooling lava field of the 2012–2013 fissure eruption at Tolbachik volcano, Kamchatka, Russia. The associated minerals are belomarinaite, tenorite, hematite, anglesite and gold. Marinaite forms prismatic, tabular, lamellar or acicular crystals up to 0.06 × 0.06 × 0.3 mm or aggregates of these forms up to 3 mm across. The mineral has a brown to black colour and submetallic lustre. Under the microscope in reflected light marinaite is grey with reddish-brown internal reflections. D(calc.)= 5.026 g/cm3. Electron microprobe analyses yielded (wt.%) 62.15 CuO, 16.71 Fe2O3, 5.11 Al2O3, 3.14 TiO2, 0.16 SiO2, 12.84 B2O3, total 100.11 wt.%. The empirical formula calculated based on 5 O apfu is Cu2.07Fe0.56Al0.27Ti0.10Si0.01B0.98O5. Marinaite is monoclinic, space group P21/c, unit-cell parameters are: a = 3.12750(18), b = 11.9690(8), c = 9.4657(5) Å, β = 97.568(6)°, V = 351.24(4) Å3 and Z = 4. The strongest lines of the powder XRD pattern [d in Å(I)(hkl)] are: 5.051(95)(021); 4.700(69)(002); 3.675(26)(031); 2.764(100)(023, $\bar 1$02, 111, 120); 2.524(94)(042); 2.444(45)(130, 102, $\bar 1$31); 2.320(31)(051, $\bar 1$13, 131); 2.037(22) (113, $\bar 1$33); 1.840(22)(044, 133, 062). Marinaite is isostructural with synthetic Cu2Fe3+O2(BO3) and has a monoclinically distorted ludwigite-type structure. The mineral is named in honour of the Russian mineralogist Marina Vsevolodovna Kuznetsova (1948–2015).

The crystal structure of Form A of dequalinium chloride has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory techniques. Dequalinium chloride Form A crystallizes in space group P42212 (#94) with a = 26.2671(8), c = 9.1119(4) Å, V = 6,286.9(4) Å3, and Z = 8 at 298 K. Despite the conventional representation of the cation, the ring N atoms are not positively charged. The positive charges are distributed on the ring carbon atoms ortho and para to these N atoms. The central decyl chain conformation is more kinked than the all-trans that might be expected in the solid state, but contains only one unusual torsion angle. The crystal structure consists of an array of dequalinium cations, with chloride anions located in regions between the cations. There are short stacks of roughly parallel rings in multiple directions. There is only one classical hydrogen bond in the structure, N–H···Cl between one of the amino groups and one of the chloride anions. Several C–H···Cl hydrogen bonds are prominent, involving ring, chain, and methyl hydrogen atoms as donors. Particularly noteworthy are the hydrogen bonds from the first and second C atoms at each end of the decyl chain. The powder pattern has been submitted to the International Centre for Diffraction Data (ICDD) for inclusion in the Powder Diffraction File™ (PDF®).

The crystal structure of protriptyline hydrochloride has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Protriptyline hydrochloride crystallizes in space group P21/n (#14) with a = 10.10772(19), b = 32.0908(6), c = 10.45302(21) Å, β = 92.8748(10)°, V = 3,386.33(15) Å3, and Z = 8 at 298 K. The crystal structure contains the expected N–H···Cl hydrogen bonds, which link the cations and anions into crankshaft-shaped chains along the c-axis. The cations and the anions form layers parallel to the ac-plane, with van der Waals interactions between the layers. The powder pattern has been submitted to the International Centre for Diffraction Data (ICDD®) for inclusion in the Powder Diffraction File™ (PDF®).

The crystal structure of racemic afoxolaner has been solved and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Afoxolaner crystallizes in space group P21/a (#14) with a = 9.6014(6), b = 14.0100(11), c = 39.477(10) Å, β = 94.389(7)°, V = 5,294.7(17) Å3, and Z = 8 at 298 K. The crystal structure consists of layers of molecules parallel to the ab-plane. The boundaries of the layers are rich in halogens. Within the layers, there is parallel stacking of rings along both the a- and b-axes. Two classical N–H···O hydrogen bonds link the two independent molecules into dimers. The powder pattern has been submitted to the International Centre for Diffraction Data (ICDD®) for inclusion in the Powder Diffraction File™ (PDF®).

BaLa2Cu1−xBaxTi2O9 (x = 0.00, 0.15, and 0.30) ceramics were synthesized in polycrystalline form via the conventional solid-state reaction techniques in air. The crystal structure of the title compositions was characterized by room-temperature X-ray powder diffraction and analyzed using the Rietveld refinement method. All the compositions crystallize in the tetragonal symmetry of space group I4/mcm (No. 140) with cell volumes: 249.43(1) Å3 for x = 0.00, 249.42(1) Å3 for x = 0.15, and 250.05(1) Å3 for x = 0.30. The tilt system of the MO6 octahedra (M = Cu(Ba2)/Ti) corresponds to the notation a0a0c−. The MO6 octahedra share the corners via oxygen atoms in 3D. Along the c-axis, the octahedra are connected by O(1) atoms of (0, 0, 1/4) positions; while in the ab-plane, they are linked by O(2) atoms of (x, x + 1/2, 0) positions. The bond angle of M–O2–M is 168.6(7)° for x = 0.00, 168.6(6)° for x = 0.15, and 166.8(6)° for x = 0.30, whereas the bond angle of M–O1–M is constrained to be 180° by space group I4/mcm.

Paramolybdomenite, ideally PbSeO3, the new mineral (IMA2023–025) dimorphous with molybdomenite, was discovered in the weathering zone of the Western paleo-fumarole field at Mountain 1004, Tolbachik volcano, Kamchatka, Russia. It is a supergene mineral associated with chrysocolla, allophane, atacamite, opal, gypsum, anglesite, linarite, brochantite, munakataite, cerussite, wulfenite, vanadinite, mottramite, volborthite, pyromorphite, fluorpyromorphite, fluorphosphohedyphane, phoenicochroite, vauquelinite, murdochite, fluorite, gearksutite and limonite. Paramolybdomenite occurs as tabular to lamellar crystals up to 0.1 × 0.05 × 0.01 mm and their clusters up to 0.15 mm. It is transparent, bright yellow, with adamantine lustre. Dcalc is 6.743 g cm–3. In reflected light, paramolybdomenite is grey; anisotropism is strong, from brownish-yellow to dark brown. The reflectance values [Rmax–Rmin,%(λ, nm)] are: 11.6–13.9(470), 11.2–11.4(546), 10.9–11.1(589), 10.6–10.7(650). Chemical composition (wt.%, electron-microprobe data) is: PbO 67.63, SeO2 26.25, SO3 5.42, total 99.30. The empirical formula calculated based on 2 Pb+Se+S apfu is Pb1.00Se4+0.78S6+0.22O3.22. Paramolybdomenite is monoclinic, P21/c, a 8.997(1), b 8.159(1), c 9.032(1) Å, β 103.33(1)°, V 645.1(1) Å3 and Z = 8. The strongest reflections of the power XRD pattern [d,Å(I)(hkl)] are: 3.897(16)(012), 3.823(17)(210), 3.534(34)($\bar 202$, $\bar 121$), 3.293(100)($\bar 120$), 3.244(63)($\bar 212$), 2.997(35)(022), 2.981(36)(220, $\bar 221$), 2.788(49)($\bar 113$, $\bar 311$, 202), and 2.760(26)(310, $\bar 302$). The crystal structure was solved from single-crystal XRD data, R = 0.112. Paramolybdomenite is a natural analogue of synthetic α-PbSeO3 whilst molybdomenite is an analogue of β-PbSeO3 (monoclinic, P21/m). In the structure of paramolybdomenite the [Pb2+O9] polyhedra are cross-connected via common edges and are connected via common corners with [Se4+O3] groups to form a quasi-framework. Selenium atoms occupy two crystallographically independent sites; the Se1 site is occupied only with Se4+, whereas Se2 has the mixed Se/S population [substitution of (SeO3)2– for (SO4)2–]. It is shown that the so-called ‘molybdomenite-P21/c’ from the El Dragón Mine, Potosí, Bolivia is in fact the second occurrence of paramolybdomenite.

The new mineral zanelliite, ideally PbCu9[AsO3.5(OH)0.5]2(AsO4)2(OH)9(H2O)3, was discovered at the Grosses Chalttal deposit, Mürtschenalp district, Glarus, Switzerland. It occurs as aggregates of {100} platy crystals, up to 0.05 mm in size, turquoise-green in colour. Lustre is vitreous. The calculated density is 4.425 g cm–3. The empirical formula, based on 28 O atoms per formula unit, is (Pb0.90Ca0.08)Σ0.98(Cu9.00Zn0.01)Σ9.01(As3.84Mo0.17)Σ4.01O15.17(OH)9.83(H2O)3. The occurrence of H2O was confirmed through micro-Raman spectroscopy and structural analysis. Zanelliite is monoclinic, space group C2/c, with unit-cell parameters a = 39.395(7), b = 5.5563(9), c = 10.5373(17) Å, β = 95.109(6)°, V = 2297.3(7) Å3 and Z = 4. The eight strongest reflections in the observed powder X-ray diffraction pattern are [d in Å (I)]: 19.7 (100), 4.86 (74), 4.48 (31), 4.28 (40), 3.777 (42), 2.964 (82), 2.708 (74), and 2.569 (37). The crystal structure of zanelliite was refined to R1 = 0.1215 for 2077 unique reflections with F > 4σ(F) and 125 refined parameters. Two different kinds of layers can be identified, i.e. a Cu–Pb–As heteropolyhedral layer, with composition [PbCu6As4O14(OH)6(H2O)], and a Cu layer, with formula [Cu3O(OH)4(H2O)2]. The crystal structure is composed of an alternating stacking of these two types of layers in a 1:1 ratio. Zanelliite is a supergene mineral whose origin is related to the oxidation of primary Cu ores. It is associated with brochantite, chrysocolla, heimite and parnauite. A second occurrence of zanelliite was reported from the Hochmättli deposit, Mürtschenalp district, Glarus, Switzerland. Zanelliite honours the mineral collector, mathematics and geography teacher Dr. Remo Zanelli (b. 1977) for his contributions to the knowledge of the secondary minerals of the ore deposits of the Glarus Alps. The mineral, its name, and its symbol (Znl) were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2024-061).