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.

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).

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.

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.

The structure of corundum is not amenable to accommodating beryllium, yet Be is commonly added to corundum for purposes of colour modification. Where the main sites in corundum are octahedrally coordinated, Be is tetrahedrally coordinated in all known Be minerals. To attempt to explain this discrepancy, the configurations of Be in the Be–Al–O±H system were determined using density functional theory (DFT). In the Be–Al–O system, the most likely Be configuration is in triangular coordination, replacing Al and bonded to three oxygen on the basal plane (large triangle) of the Al-vacant octahedral site. When H is added, OH groups form at the opposite face of the same octahedron, pointing either into or out of the site. Be–H (beryllium hydride) defects are also stable at the DFT level, with Be bonded to three O and one H. As some defects contain O–H or Be–H bonds, the DFT calculations can be corroborated by FTIR spectroscopy. Spectra recorded from 1000 corundum crystals with elevated Be confirm that bands centred at 3062 and 2490 cm–1 correspond to Be-associated defects. Polarised spectra show that the band at 2490 cm–1 resolves into two, one centred at 2491 cm–1, with a shoulder at 2523 cm–1, one of which is probably associated with a Be–H bond. The 3062 cm–1 band resolves into at least three, including a major band at 3058 cm–1, a shoulder at 3140 cm–1 and a small, sharp band at 3082 cm–1. Whilst there are caveats relating to curve fitting and baseline subtraction, the 3058 cm–1 band can probably be attributed to the defect where H points into the Al-vacant octahedral site, and the 3140 cm–1 band to the defect where the H points out. To our knowledge, this is the first occurrence of Be in triangular coordination proposed for a naturally occurring mineral. This substitution mechanism may also explain the high diffusivity of Be, as Be is effectively associated with its own Al vacancy.

Uvite, CaMg3(Al5Mg)(Si6O18)(BO3)3(OH)3(OH), is a new mineral of the tourmaline supergroup. It occurs in the Facciatoia quarry, San Piero in Campo, Elba Island, Italy (42°45′04.55″N, 10°12′50.89″E) at the centre of a narrow (2–3 cm wide) vein composed of aggregates of dark brown to black tourmaline, penetrating (magnesite + dolomite)-rich hydrothermally altered metaserpentinite. Crystals are euhedral and up to 1 cm in size, brown with a vitreous lustre, conchoidal fracture and grey streak. Uvite has a Mohs hardness of ~7½, a calculated density of 3.115 g/cm3 and is uniaxial (–). Uvite has trigonal symmetry, space group R3m, a = 15.9519(10) Å, c = 7.2222(5) Å, V = 1597.3(1) Å3 and Z = 3. The crystal structure was refined to R1 = 1.77% using 1666 unique reflections collected with MoKα X-rays. Crystal-chemical analysis resulted in the empirical crystal-chemical formula $^X ({\rm Ca}_{0.61}{\rm Na}_{{0.35}} \square_{{0.04}})_{\Sigma 1.00}{}^{Y} \left( {{\rm Mg}_{1.50}{\rm Fe}^{2 + }_{0.47} {\rm Al}_{0.71}{\rm Fe}^{3 + }_{0.14} {\rm Ti}_{0.18}} \right)_{\Sigma 3.00}$${}^{Z} \left( {{\rm Al}_{4.54}{\rm Fe}^{3 + }_{0.18} {\rm V}^{3 + }_{0.02} {\rm Mg}_{1.27}} \right)_{\Sigma 6.00}{}^{T}\left[ {{\left( {{\rm Si}_{5.90}{\rm Al}_{0.10}} \right)}_{\Sigma 6.00}{\rm O}_{18}} \right]{\rm } \left( {\rm BO_3} \right)_3^{} {^{\rm O(3)}}\left( {\rm OH} \right)_3{}^{{\rm O}\left( 1 \right)} [\left( {\rm OH} \right)_{0.55}{\rm F}_{0.05}{\rm O}_{0.40}]_{\Sigma 1.00}$

which recast in its ordered form for classification purposes is:

$$\eqalign{& ^{\rm X} ({\rm Ca}_{0.61}{\rm Na}_{0.35}\squ _{0.04})_{\Sigma 1.00}{}^{\rm Y} \left( {{\rm Mg}_{2.35}{\rm Fe}^{2 + }_{0.47} {\rm Ti}_{0.18}} \right)_{\Sigma 3.00} \cr & {}^{\rm Z} \left( {{\rm Al}_{5.25}{\rm Fe}^{3 + }_{0.32} {\rm V}^{3 + }_{0.02} {\rm Mg}_{0.42}} \right)_{\Sigma 6.00}{}^{\rm T} \left[ {{\left( {{\rm Si}_{5.90}{\rm Al}_{0.10}} \right)}_{\Sigma 6.00}{\rm O}_{18}} \right]{\rm }\left( {\rm BO_3} \right)_3{}^{\rm V} \left( {\rm OH} \right)_3{}^{\rm W} [\left( {\rm OH} \right)_{0.55}{\rm F}_{0.05}{\rm O}_{0.40}]_{\Sigma 1.00}}$$

Barium melilite – bennesherite, Ba2Fe2+Si2O7, known only from pyrometamorphic rocks of the Hatrurim Complex in Israel, has been recognised in a carbonate–silicate xenolith from the Bellerberg volcano area in Germany. The empirical formula of the German specimen is as follows: (Ba1.32Ca0.43Sr0.23Na0.05K0.02)Σ2.05(Fe2+0.79Ti0.06Mg0.05Al0.04Mn0.03Zn0.01)Σ0.98Si1.97O7. The Raman spectrum of bennesherite exhibits the presence of the main vibrations related to Fe2+O4 tetrahedra and disilicate Si2O7 groups at the T1 and T2 sites, at 589 cm–1 and in the range 618–673 cm–1, respectively. Detailed spectroscopic analyses performed for bennesherite in two different and random orientations confirm the reduction of bands intensity and the number of some components in several spectral ranges. Moreover, the presence of a heavy Ba atom indicates a decrease in band frequencies compared to melilites with Ca at the X position. A single-crystal X-ray diffraction experiment, despite attempts, could not be carried out due to the poor quality and small size of the bennesherite crystals however, a combination of composition and Raman data allowed for accurate phase identification. Detailed mineralogical investigations distinguished rare Ba minerals in association with bennesherite, such as walstromite, fresnoite and celsian, along with various ferrous melilites. Some of the detected phases are described from xenoliths of the Bellerberg volcano for the first time. The uniqueness of the Bellerberg volcano mineralisation is reflected in the interaction of alkaline magma with xenoliths of different compositions, which suggests that this locality still deserves attention as a source of new and unique minerals.

A new mineral species, franksousaite (IMA2021-096), ideally PbCu(Se6+O4)(OH)2, has been found from the El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia. It occurs as short prismatic crystals included in colourless anglesite. Associated minerals are Co-bearing krut'aite–penroseite, chalcomenite, schmiederite, olsacherite, phosgenite, anglesite and cerussite. Franksousaite is blue in transmitted light, transparent with very pale blue streak and has a vitreous lustre. It is brittle and has a Mohs hardness of 2–2½. Cleavage is perfect on {100}. The calculated density is 5.64 g/cm3. An electron microprobe analysis yielded an empirical formula (based on 6 O apfu) of Pb1.02Cu0.98[(Se0.84S0.17)Σ1.01O4)](OH)2, which is simplified to PbCu[(Se,S)O4)](OH)2.

Franksousaite is the Se6+ analogue of linarite, PbCu(SO4)(OH)2. It is monoclinic, with space group P21/m and unit-cell parameters a = 9.8208(3), b = 5.7340(2), c = 4.74980(10) Å, β = 102.683(2)°, V = 260.947(13) Å3 and Z = 2. The crystal structure of franksousaite consists of Jahn-Teller-distorted Cu2+O6 square bipyramids, which form chains along b by sharing trans edges across their square planes. The chains are decorated by SeO4 tetrahedra and linked to one another by hydrogen bonds to form layers parallel to (100). These layers are bound together by double layers of PbO8 and SeO4 polyhedra. The PbO8 polyhedron exhibits one-sided coordination typical of Pb2+ with a stereochemically active 6s2 lone-electron-pair. The major structural difference between franksousaite and linarite lies in the <Se–O> vs. <S–O> bond distances (1.615 vs. 1.482 Å), accounting for the larger unit-cell volume for franksousaite. A comparison of Raman spectra for the four minerals in the linarite group (linarite, franksousaite, munakataite and schmiederite) reveals the obvious differences among them, especially in the range from 700 to 1000 cm–1, indicative of the presence or absence of (Se4+O3)2–, (Se6+O4)2–, and/or (SO4)2– groups.

The Marepalli dyke of the Vattikod cluster of the Ramadugu Lamproite Field, Nalgonda district, Telangana, India consists of pseudomorphed leucite, phlogopite (Al-poor, Ti-rich zoned phlogopite micas), pseudomorphed olivine, fluorapatite and Al-poor diopside embedded in groundmass consisting mainly of poikilitic Fe-rich titanian phlogopite and potassic amphibole. Other groundmass minerals are Al-Na-poor diopside, Al-poor spinels (titanian magnesian chromites to titanian chromites), Sr-rich fluorapatite and late-stage interstitial anhedral crystals of titanite and K-feldspar. The late-stage deuteric minerals present are REE-rich allanite, pyrite, magnetite, chalcopyrite, galena, hydro-zircon, carbonates (calcite, witherite and strontianite), baryte and cryptocrystalline SiO2. Apatite is an early crystallising phase and is present as inclusions in phlogopite and pyroxene. Phlogopite and amphibole occur as inclusions in titanite and K-feldspar. The compositional trends of phlogopite are of almost constant Al2O3 content with FeOT and TiO2 enrichment, and are typical of lamproitic micas. The FeOT enrichment is accompanied additionally by MgO depletion (reflecting VIFe2+ enrichment) from core to rim together with a slight increase in the tetraferric iron component. Diopside is characterised by <0.4 wt.% alumina and <0.6 wt.% sodium contents and exhibits typical lamproitic affinity. The spinels are alumina-poor with un-evolved titanian magnesian chromite to titanian chromite compositions. The presence of K-richterite, as an abundant amphibole, indicates a lamproite affinity, and on the basis of the typomorphic mineralogy, this rock is classified as a ‘pseudoleucite-amphibole-phlogopite lamproite’. The Marepalli lamproite shows significant difference in compositional ranges of phlogopite, amphibole, pyroxene and spinel in comparison to those reported from the Vattikod, Gundrapalli, Ramadugu, Somavarigudem and Yacharam lamproites of Ramadugu Lamproite Field. These lamproites are considered to form from a common parent magma under reducing conditions as evidenced from: (1) low tetraferric iron content in phlogopite; (2) low Fe3+# and Ti# in spinels; and (3) high F content in phlogopite and apatite.

Saccoite, Ca2Mn3+2F(OH)8⋅0.5(SO4), is a new mineral found at the N'Chwaning III mine, Kalahari Manganese Field, Northern Cape Province, Republic of South Africa. It occurs as fillings of voids in hydrothermally altered manganese ore (comprising mostly of bixbyite and baryte). Further associated minor minerals are braunite, gypsum, chlorite, sturmanite and ettringite. Saccoite forms small needles, felted crystal masses or crusts. The new mineral is olive green, transparent, with white streak and vitreous lustre. No luminescence is observed. Saccoite is uniaxial (–) with refractive indices at 589(1) nm of ω = 1.705(5) and ɛ = 1.684(2). Pleochroism is distinct, i.e. bluish green (ω) and yellowish green (ɛ). The chemical composition was studied by means of an electron probe micro-analyser (EPMA) using wavelength-dispersive X-ray spectrometry (WDS). The empirical mineral formula is Ca2.06Mn3+1.78Cu0.10Mg0.07F0.97(OH)8.02(SO4)0.39. The unit-cell dimensions of saccoite (space group P4/ncc) are a = 12.834(3) Å, c = 5.622(2) Å, V = 926.0(4) Å3), and the calculated mass density is 2.73 g⋅cm–3. Saccoite exhibits a heteropolyhedral framework structure that is composed of edge- and corner sharing CaF2(OH)6 and M(OH)6 polyhedra (M = Mn3+ and Cu2+) with large channels along [001], which host disordered and only partially occupied groups, especially SO42–. The hydrogen atoms of the OH groups point into the channel to form hydrogen bonds with the channel anions. Ca–F distances are ~2.3 Å, the Ca–OH distances in the range of 2.44–2.58 Ǻ, and the M(OH)6 octahedron is strongly 4+2 Jahn-Teller distorted (4 × ~1.92 Å, 2 × 2.27 Å). The F atom is tetrahedrally coordinated to calcium atoms. The strongest lines in the powder X-ray diffraction pattern [d in Å (relative intensity) (hkl)] are: 9.0735 (35) (110), 4.5370 (95) (220), 4.0644 (20) (310), 3.0105 (100) (321), 2.8117 (20) (002), 2.7242 (75) (411), 1.9755 (35) (611), and 1.8142 (20) (550).

A rare earth element (REE)-, Cr- and Mg-bearing variety of the vanadium epidote-group mineral mukhinite occurs in a calcite–dolomite carbonatite dyke cutting metamorphosed volcano-sedimentary rocks exposed in the walls of the quarry of the Svetlinsky gold deposit, South Urals. This mineral was found in a paragene assemblage including native sulphur, phlogopite and fluorophlogopite, together with accessory pyrite, other sulfides and sulfosalts, gold, Cr- and V-bearing muscovite, margarite, Cr- and V-bearing dravite, fluoro-tremolite, actinolite, fluoro-pargasite, anhydrite, apatite, uranium hydroxides, V-rich titanite, V- and Nb-rich rutile, spinel and corundum. The contents of ΣREE2O3 and V2O3 in mukhinite vary in the ranges of 4.01–9.69 and 5.34–7.46 wt.%, respectively. A Raman spectrum of REE-rich mukhinite is provided. The main schemes of isomorphic substitutions in mukhinite are ΣREE + Mg ↔ Ca + Al and V+Cr ↔ Al. The crystal structure of REE-rich mukhinite has been studied by single-crystal X-ray diffraction analysis. The mineral is monoclinic, with the space group P21/m, and unit-cell parameters are: a = 8.8972(11) Å, b = 5.6221(6) Å, c = 10.1519(12) Å, β = 115.169° and V = 459.60(11) Å3. The crystal structure of REE-rich mukhinite is similar to that of its synthetic analogue; the refined crystal-chemical formula of the sample studied is (Z = 2): {A1CaA2(Ca0.8REE0.2)}{M1(Al0.95Cr0.05)M2AlM3[(V,Cr)3+0.40Al0.35Mg0.25]}(Si2O7)(SiO4)O(OH).

Tennantite-(Cd), Cu10Cd2As4S13, was approved as a new mineral species from the Berenguela mining district, Pacajes Province, La Paz, Bolivia. It occurs as black metallic anhedral grains, up to 1 mm across, associated with baryte, montmorillonite and secondary Cd-sulfates (aldridgeite, niedermayrite and voudourisite). In reflected light, tennantite-(Cd) is isotropic and grey with brownish tints. Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 30.0; 546: 30.1; 589: 28.2; and 650: 25.8. Electron microprobe analysis gave (in wt.% – average of 11 spot analyses): Cu 40.56(32), Ag 0.05(5), Fe 0.04(1), Zn 1.91(63), Cd 11.32(1.09), Hg 0.04(7), As 19.04(43), S 26.78(30), total 99.74(53). On the basis of ΣMe = 16 atoms per formula unit (apfu), the empirical formula of tennantite-(Cd) is Cu9.98Ag0.01Cd1.57Zn0.46Fe0.01As3.97S13.05. Tennantite-(Cd) is cubic, I$\bar{4}$3m, with unit-cell parameters a = 10.3088(2) Å, V = 1095.53(6) Å3 and Z = 2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1 = 0.0152 on the basis of 359 unique reflections with Fo > 4σ(Fo) and 22 refined parameters. Tennantite-(Cd) is isotypic with other tetrahedrite-group minerals. Its crystal-chemistry is discussed and previous findings of Cd-rich tetrahedrite-group minerals are briefly reviewed.

Kaznakhtite, ideally Ni6Co3+2(CO3)(OH)16⋅4H2O, is a new member of the hydrotalcite group within the hydrotalcite supergroup. The mineral was discovered at the Kaznakhtinskiy ultrabasic massif, Altai Republic, SW Siberia, Russia. It occurs as powdery aggregates forming flattened lenses up to 1.5 × 0.5 cm and veinlets up to 1 cm long and up to 1 mm thick in aggregates of chrysotile, lizardite, stichtite and dolomite. Other associated minerals include brucite, chromite, heazlewoodite, manganochromite, magnetite and magnesioferrite. Kaznakhtite aggregates are composed of tiny platy grains up to 0.01 mm across. Kaznakhtite is light green and translucent in aggregates. It has an earthy lustre and white streak. Cleavage is micaceous on {001}. Dcalc = 2.864 g cm–3. The mineral is optically uniaxial (–) with ɛ = 1.657(3) and ω = 1.676(3), and weakly pleochroic in greenish hues, ω > ɛ. Chemical composition (wt.%, electron microprobe, Co valence state determined by XANES spectroscopy, CO2 and H2O calculated by stoichiometry) is: MgO 2.15, NiO 47.40, ZnO 0.22, Al2O3 0.16, Cr2O3 0.98, Co2O3 17.42, Cl 0.63, CO2 5.05, H2O 24.60, –O=Cl –0.14, total 98.47. The empirical formula calculated based on the sum of all metal cations = 8 apfu is (Ni5.54Mg0.47Zn0.02)Σ6.03(Co3+1.83Cr0.11Al0.03)Σ1.97C1.00O2.99(OH)15.84Cl0.16⋅4H2O. Infrared spectroscopy confirmed the presence of CO32– anions, OH– groups and H2O molecules. The crystal structure was refined by the Rietveld method with RB = 0.19%. Kaznakhtite is trigonal, space group R͞3m, a = 3.0515 (3), c = 23.180 (3) Å, V = 186.93 (4) Å3 and Z = 3/8. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.72 (100) (003); 3.863 (24) (006); 2.630 (4) (101); 2.576 (10) (012); 2.294 (6) (015); 1.950 (4) (018); 1.526 (4) (110); and 1.497 (4) (113). Kaznakhtite is a Co3+ analogue of reevesite, Ni6Fe3+2(CO3)(OH)16⋅4H2O. The mineral is named after its type locality.