The new mineral ferroberaunite, Fe2+Fe3+5(PO4)4(OH)5⋅6H2O (IMA2021-36; symbol: Fbru), occurs in cavities of ‘limonite’ iron ore from the Gravel Hill mine, Perranzabuloe, Cornwall, England. Its flattened prismatic crystals up to 400 μm long are dark green to olive green, transparent to translucent, with a vitreous lustre, pearly on cleavages. The Mohs hardness is ~3–4. The density measured by the flotation method is 2.94(2) g⋅cm–3, the calculated density is 2.907 g⋅cm–3. Ferroberaunite is biaxial (–), with α = 1.736(2), β = 1.765(3), γ = 1.786(5) at 589 nm, 2Vmeas. = 68(3)°, 2Vcalc. = 79°; dispersion of optical axes is strong, r > v; orientation is Y = b; X ≈ a, Z ≈ c. Pleochroism is strong: X = bluish-green >> Z = green > Y = yellow. Electron-microprobe analyses gave the empirical formula (Fe2+0.75Ca0.01Mn0.02Fe3+0.22)Σ1.00(Fe3+4.88Al0.04)Σ4.92(PO4)4O0.11(OH)4.76⋅6H2O. Ferroberaunite is monoclinic, C2/c, with a = 20.8708(3), b = 5.1590(8), c = 19.2263(3) Å, β = 93.3186(17)°, V = 2066.7(3) Å3 and Z = 4. The eight strongest lines in the powder X-ray diffraction pattern are [dmeas, Å (Irel., %) (hkl)]: 10.410 (100) (200), 9.606 (14) (002), 7.271 (11) (20$\bar{2}$), 5.203 (4) (400), 3.467 (12) (600), 3.325 (6) (60$\bar{2}$), 3.201 (6) (006), 2.600 (4) (800). The mineral is isostructural with beraunite, redefined recently as Fe3+6(PO4)4O(OH)4⋅6H2O.

Garpenbergite is a new mineral (IMA2020-099) from the Garpenberg Norra mine, Hedemora, Dalarna, Sweden. It occurs with carlfrancisite and minor stibarsen, paradocrasite and filipstadite in a fractured skarn matrix of granular jacobsite, alleghanyite, kutnohorite and dolomite. Crystals are short-prismatic, up to 1.5 mm in length. They have a blackish to greyish brown colour, and are lustrous semi-opaque, with brown streak. Garpenbergite is brittle, with an uneven to subconchoidal fracture. Cleavage is distinct on {010}. Hardness ≈ 5 (Mohs) and VHN100 = 650(40). Dcalc = 4.47(1) g⋅cm−3, overall ncalc = 1.85. Maximum specular reflectance values (%) obtained are 9.2 (470 nm), 9.1 (546 nm), 9.0 (589 nm) and 8.9 (650 nm). The empirical chemical formula of garpenbergite, based on electron microprobe data, is (Mn2+3.97Mg1.48Mn3+0.26Zn0.29)Σ6.00(As0.89Fe3+0.04Mn3+0.06Si0.01)Σ1.00(Sb0.98Fe0.02)Σ1O10[(OH)1.99Cl0.01]Σ2.00. The five strongest Bragg peaks in the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are 3.05 (30) (002), 2.665 (100) (161), 2.616 (40) (301), 2.586 (25) (251) and 1.545 (45) (462). The orthorhombic unit-cell dimensions (in Å) are a = 8.6790(9), b = 18.9057(19) and c = 6.1066(6), with V = 1001.99(18) Å3 for Z = 4. The crystal structure was refined from single-crystal X-ray diffraction data in the space-group Ibmm to R1 = 3.7% for 957 reflections. Garpenbergite, ideally Mn6As5+Sb5+O10(OH)2, is isostructural with manganostibite, Mn7AsSbO12, but possesses a cation vacancy (□) at an octahedrally coordinated structural site; the two minerals are thus related by the exchange Mn2+ + 2O2– → □ + 2(OH)–. The presence of hydroxyl groups is supported by vibration bands at 3647 and 3622 cm−1 in the Raman spectrum of garpenbergite and by bond-valence considerations.

The Palaeoproterozoic (~2.0−1.8 Ga) Stankuvatske Li deposit (Ukrainian Shield, Central Ukraine) represents an uncommon case of recrystallised, fine-grained petalite ± spodumene meta-pegmatite dykes with LCT affinity hosted in amphibolites and meta-ultrabasic rocks. The meta-pegmatite dykes show remnants of primary, pre-metamorphic zoning, with dominant magmatic albite, K-feldspar, quartz, Li-phases (petalite, spodumene, rarely triphylite and montebrasite), and accessory muscovite, fluorapatite, columbite-(Fe), tantalite-(Fe), cassiterite, Ta-rich rutile, zinco- and ferronigerite, gahnite, pyrite, sphalerite and zircon. The parental magma of the meta-pegmatites was peraluminous, and enriched in Li and P, though relatively poor in B and F during the late-magmatic stage. Metasomatic reactions between residual pegmatite magma and (ultra)basic country rocks resulted in the precipitation of holmquistite, triphylite, fluorapatite, tourmaline and Rb–Cs-rich biotite. Secondary generations of fine-grained petalite, spodumene, albite and K-feldspar were formed during post-magmatic stages, i.e. during hydrothermal–metasomatic alteration and/or subsequent tectono–metamorphic recrystallisation of the primary pegmatites. The initial subsolidus metasomatism of primary feldspars took place in alkaline conditions as a result of Na (partly K) for Li exchange.

The presence of fibrolitic sillimanite and chrysoberyl, together with the scarcity of muscovite and (OH,F)-bearing minerals, point to metamorphic recrystallisation of the former Li-rich granitic pegmatites at relatively high-temperature and medium-pressure (~600±50°C; ~0.3−0.4 GPa) conditions.

The beryllium silicate minerals phenakite and bertrandite have been identified in granitic pegmatite dykes of the beryl-columbite subtype of Variscan age (~340−355 Ma), associated with S- to I-type granitic rocks of the Tatric Superunit, Western Carpathians (Slovakia). The two beryllium silicates and associated minerals were characterised by electron microprobe analysis, back-scattered electron petrography and cathodoluminescence imagery, X-ray diffraction and micro-Raman techniques. Phenakite and bertrandite form euhedral-to-anhedral crystals and aggregates in irregular domains and veinlets replacing primary magmatic beryl. A detailed textural study revealed a close genetic association of phenakite and bertrandite with secondary fine-grained quartz, K-feldspar and muscovite. Locally, clay phyllosilicate minerals, (with compositions similar to those of Fe-dominant hydrobiotite, beidellite, nontronite and saponite) occur as the youngest minerals. During the post-magmatic (hydrothermal) stage of the pegmatites, infiltration of aqueous K-bearing fluids at T ≈ 200–400°C resulted in the breakdown of magmatic beryl to secondary assemblages containing phenakite and bertrandite.

The complexities of chemical composition and crystal structure are fundamental characteristics of minerals that have high relevance to the understanding of their stability, occurrence and evolution. This review summarises recent developments in the field of mineral complexity and outlines possible directions for its future elaboration. The database of structural and chemical complexity parameters of minerals is updated by H-correction of structures with unknown H positions and the inclusion of new data. The revised average complexity values (arithmetic means) for all minerals are 3.54(2) bits/atom and 345(10) bits/cell (based upon 4443 structure reports). The distributions of atomic information amounts, chemIG and strIG, versus the number of mineral species fit the normal modes, whereas the distributions of total complexities, chemIG,total and strIG,total, along with numbers of atoms per formula and per unit cell are log normal. The three most complex mineral species known today are ewingite, morrisonite and ilmajokite, all either discovered or structurally characterised within the last five years. The most important complexity-generating mechanisms in minerals are: (1) the presence of isolated large clusters; (2) the presence of large clusters linked together to form three-dimensional frameworks; (3) formation of complex three-dimensional modular frameworks; (4) formation of complex modular layers; (5) high hydration state in salts with complex heteropolyhedral units; and (6) formation of ordered superstructures of relatively simple structure types. The relations between symmetry and complexity are considered. The analysis of temporal dynamics of mineralogical discoveries since 1875 with the step of 25 years show the increasing chemical and structural complexities of human knowledge of the mineral kingdom in the history of mineralogy. In the Earth's history, both diversity and complexity of minerals experience dramatic increases associated with the formation of Earth's continental crust, initiation of plate tectonics and the Great Oxidation event.

The new mineral nafeasite (IMA2021-103), NaFe3+(AsO3OH)2⋅H2O, was found at the Torrecillas mine, Iquique Province, Chile, where it is a secondary alteration phase associated with anhydrite, gypsum, halite, lavendulan, magnesiokoritnigite and natrojarosite. Nafeasite occurs in tightly intergrown aggregates of equant crystals. Crystals are light to medium pink and transparent, with vitreous lustre and white streak. The Mohs hardness is ~2½. The density is 3.23(2) g⋅cm–3. Optically, nafeasite is biaxial (+), with α = 1.679(3), β = 1.682(3), γ = 1.730(5) (white light); 2V = 27(2)°; and slight r < v dispersion. The empirical formulae of the holotype and cotype (based on 9 O atoms per formula unit) are Na0.98K0.02Fe0.92Al0.07As2.00O9H4.01 and Na0.97Fe0.68Al0.33As2.00O9H4.01, respectively. Nafeasite is monoclinic, space group C2, with cell parameters: a = 18.6876(16), b = 8.6769(7), c = 14.8100(10) Å, β = 105.238 (5)°, V = 2317.0(3) Å3 and Z = 12. The structure, refined to R1 = 5.03% for 5979 Io > 2σI reflections, is based on a loose 3D framework of alternating AsO3OH tetrahedra and Fe3+O6 octahedra.

Grandviewite is redefined on the basis of a reinvestigation of the holotype specimen from the Grandview mine, Arizona, USA, and additional specimens found in the Restauradora vein at the Capillitas mine, northwestern Argentina. Grandviewite from the Capillitas mine forms globular masses up to a couple of millimetres in diameter, formed by very thin platy to acicular lath-like crystals, greenish-pale blue in colour, pleochroic (X = colourless, Y = very pale blue and Z = greenish-pale blue), with pale blue streak and silky to a satiny lustre. Results of an electron-microprobe study and crystal-structure determination lead to the new ideal formula Cu3Al2(SO4)(OH)10⋅H2O, which requires (in wt.%) CuO 45.13, Al2O3 19.28, SO3 15.14, and H2O 20.45, total 100.00. Its empirical formulas are (Cu2.96Mn0.01)Σ2.97Al2.03(SO4)0.97(SiO4)0.03(AsO4)0.01(OH)9.97Cl0.01⋅H2O (Grandview mine) and Cu2.97(Al2.03Fe0.01)Σ2.04(SO4)0.95(SiO4)0.03(AsO4)0.01(PO4)0.01(OH)9.97Cl0.01⋅H2O (Capillitas mine). Grandviewite is triclinic, P$\bar{1}$, with unit-cell parameters refined from powder X-ray diffraction data: a = 5.713(2), b = 10.1374(8), c = 10.9791(9) Å, α = 72.240(6)°, β = 82.79(2)°, γ = 86.07(2)°, V = 600.5(3) Å3 and Z = 2 (Grandview mine); and a = 5.749(3), b = 10.1388(13), c = 10.9656(16) Å, α = 72.344(1)°, β = 82.83(4)°, γ = 86.77(3)°, V = 604.2(3) Å3 and Z = 2 (Capillitas mine). The crystal structure of grandviewite from the Capillitas mine was solved by 3-dimensional electron diffraction analysis (R(obs)/wR(obs) = 0.1304/0.1316 for 6401/31007 observed reflections with I ≥ 3σ(I). Grandviewite contains infinite AlO6–Cu1–AlO6 slabs along a connected on both ends to Cu2 [4 + 1]–SO4 chains. The SO4 tetrahedra form a disordered chain along a connected to the Cu2 pyramids on one side and are otherwise stabilised by strong hydrogen bonds to surrounding units. The Raman and infrared spectra for samples from both occurrences are identical. The redefinition (new chemical formula and triclinic symmetry) has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (number 21-K).

Gachingite, Au(Te1–xSex), 0.2 ≈ x ≤ 0.5, is a new mineral discovered in the Gaching ore occurrence of the Maletoyvayam epithermal deposit, Kamchatka, Russia. Gachingite forms individual droplet-like grains of sizes from 2 to 10 μm included in native gold (Au–Ag), associated with calaverite, maletoyvayamite, watanabeite and Au–Sb oxides. The aggregates do not exceed 100 μm in diameter. In plane-polarised light, gachingite is grey with a bluish tint, has bireflectance (bluish-grey to deep grey), and strong anisotropy with rotation tints blue to dark blue to brown. Reflectance values for gachingite in air (Rmin, Rmax in %) are: 39.9, 40.3 at 470 nm; 41.6, 43.3 at 546 nm; 42.0, 43.7 at 589 nm; and 43.0, 44.0 at 650 nm. Eighteen electron-microprobe analyses of gachingite gave an average composition: Au 62.40, Ag 0.57, Se 9.78, Te 27.33 and S 0.01, total 100.09 wt.%, corresponding to the formula (Au0.96Ag0.02)Σ0.98(Te0.65Se0.37)Σ1.02 based on 2 apfu, the simplified formula is Au(Te0.65Se0.35); the average analyses of its synthetic analogue is Au 65.7, Se 13.1 and Te 21.1, total 99.9 wt.%, corresponding to Au1.00(Te0.50Se0.50). The calculated density is 10.47 g/cm3. The mineral is orthorhombic, space group Cmce (#64) with a = 7.5379 Å, b = 5.7415 Å, c = 8.8985 Å, V = 385.12 Å3 and Z = 8. The crystal structure was solved and refined from the single-crystal X-ray-diffraction data of synthetic Au1.00(Te0.50Se0.50). The crystal structure of gachingite represents a unique structure type, containing linear [Au–Au–Au] chains running along the b-axis indicating strong metallic interaction in one direction. The structural identity of gachingite and its synthetic analogue Au1.00(Te0.50Se0.50) was confirmed by electron back-scatter diffraction and Raman spectroscopy. The formation of gachingite requires an abundant source of Au and Se and a high oxidising environment. Gachingite is related to the gold-bearing productive stage of ore mineralisation, which is stable at 250°C in log$f_{{\rm S}{\rm e}_ 2}$ range of −12.4 and −5.7. The mineral is named after its type locality.

Reaphookhillite, ideally MgZn2(PO4)2⋅4H2O, is a new phosphate mineral from Reaphook Hill, Flinders Ranges, South Australia, Australia. Reaphookhillite occurs as colourless, bladed to thin tabular crystals to 0.6 mm across. Cleavage is perfect parallel to {010}. The mineral occur as overgrowths on parahopeite crystals and is associated with scholzite, leucophosphite and chalcophanite. The calculated density is 3.09 g/cm3 from the empirical formula. Reaphookhillite is optically biaxial (+), α = 1.583(3), β = 1.596(3), γ = 1.611(3) and 2Vcalc = 88.7°. Electron microprobe analyses gave ZnO 41.57, MgO 7.96, MnO 0.40, P2O5 33.72, H2O(calc) 16.92, total 100.57 wt.%. The empirical formula, based on 12 O apfu, is Mg0.83Zn2.16Mn2+0.02(PO4)2.01⋅3.97H2O. Reaphookhillite is triclinic, P${\bar 1}$, with the unit-cell parameters of a = 5.7588(12), b = 7.5341(15) c = 5.2786(11) Å, α = 93.44(3), β = 91.27(3), γ = 91.30(3)°, V = 228.49(8) Å3 and Z = 1. The strongest eight lines in the powder X-ray diffraction pattern are [dobs in Å (I) (hkl)] 7.577 (100) (010); 4.461 (24) (01${\bar 1}$); 4.461 (24) (01${\bar 1}$); 3.771 (14) (020); 3.158 (13) (02${\bar 1}$); 2.982 (32) (021); 2.880 (27) (200); 2.775 (14) (1${\bar 2}$1, 12${\bar 1}$); and 2.668 (13) (1${\bar 2}{\bar 1}$, 210). Reaphookhillite is isostructural with parahopeite, with Mg replacing Zn in the 6-coordinated site in the structure. The structure contains ZnO4 and PO4 tetrahedra which share corners to form a sheet in the (001) plane. Sheets are linked in the c direction by corner sharing MgO2(H2O)4 octahedra.

The response of garnet and zircon to prograde amphibolite-facies metamorphism in late Proterozoic mica schists from the Scottish Highlands has been investigated. Spatial analysis of zircon populations using scanning electron microscopy was undertaken in Dalradian Schists that have undergone a sequence of prograde garnet growth and localised breakdown reactions involving coupled dissolution–reprecipitation. Fluid availability and matrix permeability strongly control this metamorphic response and different generations of garnet contain radically different populations of metamorphic micro-zircon and associated changes in the detrital zircon population. Micro-zircon abundance increases during garnet growth, whereas that of detrital zircon decreases. The mineralogy of the matrix influences zircon abundance in porphyroblast phases, where garnet overgrows a micaceous matrix zircon-rich garnet forms and where it overgrows a quartzofeldspathic matrix the result is zircon-poor garnet. Following garnet growth, micro-zircon abundance decreases at each stage of the prograde reaction history, with sillimanite-zone schists containing the lowest abundance, suggesting micro-zircons are texturally less stable at staurolite- and sillimanite-grade metamorphism. Micro-zircons are distributed evenly across host minerals in the matrix, with the exception of retrograde chlorite where micro-zircons are absent due to fluids removing Zr before new zircon can precipitate. There is an overall decrease in the mode of zircon at each stage of the reaction history, indicating that zircon is a highly reactive phase during amphibolite-facies metamorphism and is very sensitive to individual prograde and retrograde reactions.

Magnetite is a common mineral in the Paleoproterozoic Stollberg Zn–Pb–Ag plus magnetite ore field (~6.6 Mt of production), which occurs in 1.9 Ga metamorphosed felsic and mafic rocks. Mineralisation at Stollberg consists of magnetite bodies and massive to semi-massive sphalerite–galena and pyrrhotite (with subordinate pyrite, chalcopyrite, arsenopyrite and magnetite) hosted by metavolcanic rocks and skarn. Magnetite occurs in sulfides, skarn, amphibolite and altered metamorphosed rhyolitic ash–siltstone that consists of garnet–biotite, quartz–garnet–pyroxene, gedrite–albite, and sericitic rocks. Magnetite probably formed from hydrothermal ore-bearing fluids (~250–400°C) that replaced limestone and rhyolitic ash–siltstone, and subsequently recrystallised during metamorphism. The composition of magnetite from these rock types was measured using electron microprobe analysis and LA–ICP–MS. Utilisation of discrimination plots (Ca+Al+Mn vs. Ti+V, Ni/(Cr+Mn) vs. Ti+V, and trace-element variation diagrams (median concentration of Mg, Al, Ti, V, Co, Mn, Zn and Ga) suggest that the composition of magnetite in sulfides from the Stollberg ore field more closely resembles that from skarns found elsewhere rather than previously published compositions of magnetite in metamorphosed volcanogenic massive sulfide deposits. Although the variation diagrams show that magnetite compositions from various rock types have similar patterns, principal component analyses and element–element variation diagrams indicate that its composition from the same rock type in different sulfide deposits can be distinguished. This suggests that bulk-rock composition also has a strong influence on magnetite composition. Principal component analyses also show that magnetite in sulfides has a distinctive compositional signature which allows it to be a prospective pathfinder mineral for sulfide deposits in the Stollberg ore field.

Parahibbingite [β-Fe2(OH)3Cl], a new mineral recently described from ultramafic rocks in the Bushveld Complex, South Africa, has been found to form millimetric well-developed crystals as a terrestrial weathering product of the Muonionalusta iron meteorite. The mineral, initially identified by means of Raman spectroscopy, was found in a small cavity within a crust of rust on a granitic rock fragment that was in direct contact with the alteration crust of a meteorite specimen, collected in the Kitkiöjärvi area, Sweden. Its crystal structure was refined from single-crystal X-ray diffraction data (R1 = 0.0331) in the space group R$\bar{3}$m [a = 6.9362(4), c = 14.673(1) Å and V = 611.35(7) Å3 for Z = 6], thus confirming the structural model of synthetic β-Fe2(OH)3Cl. It consists of a network of octahedrally coordinated Fe2+ atoms alternately arranged in triangular and Kagomé layers, stacked along the c axis. The H atom position was determined, showing O–H⋅⋅⋅Cl bonds, which provides a further link between layers. Parahibbingite is found to be not only an important constituent of the corrosion system of archaeological iron artefacts but can also play an important role as an alteration product of iron meteorites.

On the western part of the eastern Indian shield, Archaean basement (Bonai granite) is overlain by radioactive conglomerate. The conglomerate contains well-rounded, fractured Mg-poor (<0.18 wt.% MgO), Al-rich (up to 21.14 wt.% Al2O3) Zn-rich chromite (>35.0 wt.% Cr2O3) containing up to 15.5 wt.% ZnO. This is the first reported occurrence of detrital zinc-rich chromite having such unusually high ZnO from India, and to our knowledge, the third reported occurrence in radioactive quartz-pebble conglomerate after Witwatersrand, South Africa and Tarkwa, Ghana. Zinc-rich chromite grains are either clean or contain exsolution blebs/lamella of rutile. The conglomerates show evidence for post-depositional hydrothermal fluid influx and fluid-induced mineral alteration. The strong negative correlation between Zn and Fe2+, Al and Cr, and Al and Fe3+, and strong positive correlation between Zn and Al suggest secondary incorporation of Zn and Al by substitution of Fe2+ and Cr (and Fe3+), respectively, leading to partial transformation of (Fe)(Cr,Al,Fe3+)2O4 towards ZnAl2O4 composition. The chromite grains were possibly derived from komatiite. The timing of Zn enrichment, either at the provenance prior to sedimentation, or at the depositional site post-dating sedimentation, remains unresolved.

The new mineral paramarkeyite (IMA2021-024), Ca2(UO2)(CO3)3⋅5H2O, was found in the Markey mine, San Juan County, Utah, USA, where it occurs as a secondary phase on gypsum-coated asphaltum in association with andersonite, calcite, gypsum and natromarkeyite. Paramarkeyite crystals are transparent, pale green-yellow, striated tablets, up to 0.11 mm across. The mineral has white streak and vitreous lustre. It exhibits moderate bluish-white fluorescence (405 nm laser). It is very brittle with irregular, curved fracture and a Mohs hardness of 2½. It has an excellent {100} cleavage and probably two good cleavages on {010} and {001}. The measured density is 2.91(2) g cm–3. Optically, the mineral is biaxial (–) with α = 1.550(2), β = 1.556(2), γ = 1.558(2) (white light); 2V = 60(2)°; strong r > v dispersion; orientation: Y = b; nonpleochroic. The Raman spectrum exhibits bands consistent with UO22+, CO32– and O–H. Electron microprobe analysis provided the empirical formula (Ca1.83Na0.20Sr0.03)Σ2.05(UO2)(CO3)3⋅5H2O (+0.07 H). Paramarkeyite is monoclinic, P21/n, a = 17.9507(7), b = 18.1030(8), c = 18.3688(13) Å, β = 108.029(8)°, V = 5676.1(6) Å3 and Z = 16. The structure of paramarkeyite (R1 = 0.0647 for 6657 I > 2σI) contains uranyl tricarbonate clusters that are linked by Ca–O polyhedra to form heteropolyhedral layers. The structure of paramarkeyite is very similar to those of markeyite, natromarkeyite and pseudomarkeyite.

The new mineral scenicite (IMA2021-057), [(UO2)(H2O)2(SO4)]2⋅3H2O, was found in the Green Lizard, Giveaway–Simplot, Markey and Scenic mines, White Canyon district, San Juan County, Utah, USA, where it occurs as a secondary phase on granular quartz matrix in association with various combinations of deliensite, gypsum, natrozippeite, rietveldite and shumwayite. Scenicite crystals are transparent, light green yellow, poorly formed blades or prisms, up to 0.1 mm in length. The mineral has white streak and vitreous lustre. It exhibits bright greenish-white fluorescence (405 nm laser). It is brittle with irregular, curved fracture and a Mohs hardness of ~2. It has excellent {100} and good {001} cleavages. The calculated density is 3.497 g cm–3. Optically, the mineral is biaxial (–) with α = 1.556(2), β = 1.573(2), γ = 1.576(2) (white light); 2V = 45(3)°; extreme r < v dispersion; orientation: X = c, Y = a, Z = b; pleochroism: X and Y = colourless, Z = light green–yellow; and X = Y < Z. The Raman spectrum exhibits bands consistent with UO22+, SO42– and O–H. Electron microprobe analysis provided the empirical formula U1.996S2.005O19H13.997. The five strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 7.69(70)(201), 5.63(100)(111), 4.92(84)(202,310), 4.80(93)(401) and 3.398(55)(020,120,511,601). Scenicite is orthorhombic, Pca21, a = 21.2144(15), b = 6.8188(3) c = 11.2554(6) Å, V = 1628.18(16) Å3 and Z = 4. In the structure of scenicite (R1 = 0.0365 for 1259 I > 2σI), linkages of pentagonal bipyramids and tetrahedra form an infinite neutral [(UO2)(SO4)(H2O)2] chain. The structure of shumwayite contains topologically identical chains.

The new mineral flaggite (IMA2021-044), Pb4Cu2+4Te6+2(SO4)2O11(OH)2(H2O), occurs at the Grand Central mine in the Tombstone district, Cochise County, Arizona, USA, in cavities in quartz matrix in association with alunite, backite, cerussite, jarosite and rodalquilarite. Flaggite crystals are lime-green to yellow-green tablets, up to 0.5 mm across. The mineral has a very pale green streak and adamantine lustre. It is brittle with irregular fracture and a Mohs hardness of ~3. It has one excellent cleavage on {010}. The calculated density is 6.137 g cm–3. Optically, the mineral is biaxial (+) with α = 1.95(1), β = 1.96(1), γ = 2.00(1) (white light); 2V = 54(2)°; pleochroism: X green, Y light yellow green, Z nearly colourless; X > Y > Z. The Raman spectrum exhibits bands consistent with TeO6 and SO4. Electron microprobe analysis provided the empirical formula Pb3.88Cu2+3.89Te6+2.08(SO4)2O11(OH)2(H2O) (–0.03 H). Flaggite is triclinic, P1, a = 9.5610(2), b = 9.9755(2), c = 10.4449(3) Å, α = 74.884(1), β = 89.994(1), γ = 78.219(1)°, V = 939.97(4) Å3 and Z = 2. The structure of flaggite (R1 = 0.0342 for 5936 I > 2σI) contains hexagonal-close-packed, stair-step-like layers comprising TeO6 octahedra and Jahn-Teller distorted CuO6 octahedra. The layers in the structure of flaggite are very similar to those in bairdite, timroseite and paratimroseite.

Dendoraite-(NH4), (NH4)2NaAl(C2O4)(PO3OH)2(H2O)2, is a new mineral species from the Rowley mine, Maricopa County, Arizona, USA. It occurs in an unusual bat-guano-related, post-mining assemblage of phases that include a variety of vanadates, phosphates, oxalates and chlorides, some containing NH4+. Other secondary minerals found in association with dendoraite-(NH4) are antipinite, fluorite, mimetite, mottramite, relianceite-(K), rowleyite, salammoniac, struvite, vanadinite, willemite, wulfenite and at least one other new mineral. Crystals of dendoraite-(NH4) are colourless blades up to ~0.1 mm in length. The streak is white and lustre is vitreous, Mohs hardness is 2½, tenacity is brittle and fracture is splintery. The calculated density is 2.122 g⋅cm–3. Dendoraite-(NH4) is optically biaxial (–) with α = 1.490(5), β = 1.540(5) and γ = 1.541(5) (white light); 2Vcalc = 15.7°; and orientation X = b. Electron microprobe analysis gave the empirical formula [(NH4)1.48K0.52]Σ2.00Na0.96(Al0.96Fe3+0.03)Σ0.99(C2O4)[PO2.97(OH)1.03]2(H2O)2, with the C, N and H contents constrained by the crystal structure. Dendoraite-(NH4) is monoclinic, P21/n, with a = 10.695(6), b = 6.285(4), c = 19.227(12) Å, β = 90.933(10)°, V = 1292(2) Å3, and Z = 4. The structural unit in the crystal structure of dendoraite-(NH4) (R1 = 0.0467 for 1322 Io > 2σI reflections) is a double-strand chain of corner-sharing AlO6 octahedra and PO3OH tetrahedra decorated by additional PO3OH tetrahedra and C2O4 groups. Topologically, this is the same chain found in the structure of thebaite-(NH4). The decorated chains connect to one another through links to NaO7(H2O) polyhedra to form a [Na(H2O)Al(C2O4)(PO3OH)2]2– sheet, which connect to one another through bonds to (NH4)/K and through hydrogen bonds.

The new alluaudite-group mineral khrenovite with the ideal, end-member formula Na3Fe3+2(AsO4)3 was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite-group sulfates, badalovite, calciojohillerite, nickenichite, johillerite, tilasite, svabite, achyrophanite, ozerovaite, pansnerite, arsenatrotitanite, anhydrite, sanidine, hematite, cassiterite, rutile and pseudobrookite. Khrenovite occurs as coarse prismatic crystals up to 0.2 × 0.3 × 0.8 mm and their clusters up to 1 mm across. It is transparent, honey-coloured, red-, orange- or yellow-brown, with vitreous lustre. Khrenovite is brittle, cleavage was not observed. Dcalc is 4.257 g cm–3. Khrenovite is optically biaxial (+), α = 1.825(7), β = 1.834(7), γ = 1.845(7) and 2Vmeas. = 80(10)°. The chemical composition (wt.%, electron-microprobe) is: Na2O 11.47, K2O 1.23, CaO 0.18, MgO 0.01, MnO 4.10, CuO 4.27, ZnO 1.99, Al2O3 0.17, Fe2O3 21.12, SiO2 0.08, P2O5 0.01, V2O5 0.10, As2O5 56.03, SO3 0.02, total 100.78. The empirical formula calculated on the basis of 12 O apfu is (Na2.26K0.16Ca0.02Mn0.35Cu0.33Zn0.15Al0.02Fe3+1.62)Σ4.91(As2.98Si0.01V0.01)Σ3.00O12. Khrenovite is monoclinic, C2/c, a = 12.2394(7), b = 12.7967(5), c = 6.6589(4) Å, β = 112.953(7)°, V = 960.37(10) Å3 and Z = 4. The crystal structure was solved from single-crystal X-ray diffraction data with R1 = 0.0287. Khrenovite is isostructural with other alluaudite-group minerals. Its structural formula simplified to the species-defining constituents is A(1)NaA(2)’NaM(1)NaM(2)Fe3+2(TAsO4)3. The mineral is named in honour of the Russian volcanologist and geologist Anatoly Petrovich Khrenov (1946–2016).

Nickolayite, FeMoP, is a new terrestrial phosphide structurally related to allabogdanite (high-pressure modification of (Fe,Ni)2P), and the meteoritic phosphides florenskyite, FeTiP and andreyivanovite, FeCrP. From the point of view of chemical composition, nickolayite is an Fe-analogue of monipite, MoNiP. The mineral was discovered in the Daba-Siwaqa complex, Central Jordan, a part of the pyrometamorphic Hatrurim Formation (the Mottled Zone), whose outcrops encompass a 150 × 200 km area around the Dead Sea in the Middle East. Nickolayite appears as an accessory phase in the fused clinopyroxene–plagioclase rocks texturally resembling gabbro–dolerite. The irregularly shaped grains of the mineral, up to 80 μm in size are associated with baryte, tridymite, chromite, hematite, pyrrhotite, fluorapatite, titanite and powellite. Macroscopically, nickolayite grains possess light-grey to greyish-white colour and metallic lustre. The mineral is ductile. The mean VHN hardness (50 g load) is 538 kg mm–2. The calculated density based on the empirical formula and the unit-cell parameters is 7.819 g cm–1. In reflected light, nickolayite has a white colour, with no bireflectance or pleochroism. The COM approved reflectance values [Rmax/Rmin (%), λ(nm)] are: 48.5/46.5 (470), 50.5/48.5 (546), 51.8/49.9 (589) and 53.9/52.0 (650). The chemical composition of the holotype crystal is (electron microprobe, average of 4 analyses, wt.%): Fe 32.21, Mo 47.06, Ni 3.69, Co 0.13, P 17.45, total 100.54, that corresponds to the empirical formula Fe1.00(Mo0.87Ni0.11Fe0.02)Σ1.00P1.00 and an ideal formula of FeMoP. Nickolayite is orthorhombic, space group Pnma, unit-cell parameters of holotype material are: a = 5.9519(5), b = 3.7070(3), c = 6.8465(6) Å, V = 151.06(2) Å3 and Z = 4. The crystal structure of holotype material was solved and refined to R1 = 0.0174 based on 251 unique observed reflections. The origin of the mineral is probably connected to the processes of co-reduction of molybdenum- and phosphorus-bearing minerals during high-temperature pyrometamorphic processes.