Rundqvistite-(Ce), ideally Na3(Sr3Ce)(Zn2Si8O24), is a new mineral from the Darai-Pioz alkaline massif, Tien-Shan Mountains, Tajikistan. The mineral occurs as elongated grains up to 0.1 mm long and up to 0.03 mm thick embedded in quartz–pectolite aggregate in a silexite-like peralkaline pegmatite. Associated minerals are quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite. The mineral is colourless with a vitreous lustre and a white streak, brittle, Dmeas. is 3.70(2) and Dcalc. is 3.709 g/cm3. Rundqvistite-(Ce) is monoclinic, space group P21/c, a = 5.1934(16), b = 7.8934(16), c = 26.011(5) Å, β = 90.02(3)° and V = 1066.3(4) Å3. The chemical composition of rundqvistite-(Ce) is SiO2 40.17, La2O3 2.64, Ce2O3 7.55, Pr2O3 0.80, Nd2O3 2.43, Sm2O3 0.33, Eu2O3 0.09, Gd2O3 0.24, Tb2O3 0.18, Dy2O3 0.21, PbO 1.03, SrO 19.83, FeO 0.37, ZnO 13.08, CaO 2.55, Na2O 8.04, total 99.54 wt.%. The empirical formula calculated on 24 O apfu (atoms per formula unit) is Na3.10Sr2.29Ca0.54Pb0.06(Ce0.55La0.19Nd0.17Pr0.06Sm0.02Gd0.02Eu0.01Tb0.01Dy0.01)Σ1.04Zn1.92Fe0.06 Si8.00O24 Z = 2. The structural formula based on refined site-occupancies is (Na2.94Sr0.06)Σ3.00 [(Sr2.23Ca0.54Pb0.06Na0.13)Σ2.96Ln3+1.04]Σ4.00[(Zn1.92Fe2+0.06)Σ1.98Si8O24], where Ln3+1.04 = (Ce0.55La0.19Nd0.17Pr0.06Sm0.02Gd0.02Eu0.01Tb0.01Dy0.01)Σ1.04. The crystal structure of rundqvistite-(Ce) was refined to R1 = 2.76% on the basis of 3184 unique reflections [F > 4σ|F|]. In rundqvistite-(Ce), the main structural unit is a (Zn2Si8O24)12– sheet parallel to (100). In the sheet, the Si and Zn tetrahedra form four-, five- and eight-membered rings. The interstitial cations at the Na and M(1–3) sites sum to [Na3(Sr3Ce)]12– apfu. The Na and M(1–3) polyhedra share common edges to form a layer. Rundqvistite-(Ce) is a structural analogue of vladykinite, ideally Na3Sr4(Fe2+Fe3+)Si8O24. Rundqvistite-(Ce) and vladykinite are related by the following substitution: [8]Ce3+ + [4](Zn2+)2 ↔ [8]Sr2+ + [4](Fe2+Fe3+). The mineral is named after Dmitry Vasilievich Rundqvist (1930–2022), a prominent Russian geologist and an expert on the geology of ore deposits, metallogeny and mineralogy of Precambrian rocks.

Kalyuzhnyite-(Ce), ideally NaKCaSrCeTi(Si8O21)OF(H2O)3, is a new mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan. It occurs as equant grains up to 0.05 × 0.07 mm in a quartz–pectolite aggregate in a silexite-like peralkaline pegmatite. Associated minerals are quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite. The mineral is colourless with a vitreous lustre and a white streak, and Dcalc. is 3.120 g/cm3. Kalyuzhnyite-(Ce) is monoclinic, P2/c, a = 18.647(4), b = 11.214(2), c = 14.642(3) Å, β = 129.55(3)° and V = 2360.9(11) Å3. The chemical composition of kalyuzhnyite-(Ce) is Nb2O5 0.53, TiO2 0.16, SiO2 43.85, Er2O3 0.13, Ho2O3 0.10, Gd2O3 0.09, Sm2O3 0.47, Nd2O3 6.22, Pr2O3 1.21, Ce2O3 6.34, La2O3 0.82, PbO 4.90, BaO 0.85, SrO 11.39, CaO 1.86, Cs2O 3.80, K2O 1.59, Na2O 2.99, H2O 5.24, F 1.55, O = F –0.65, total 100.31 wt.%. The empirical formula calculated on 26.11 (O + F) apfu is Na1.07K0.37Cs0.30Sr1.21Ca0.37Pb0.24Ba0.06(Ce0.43Nd0.41Pr0.08La0.06Sm0.03Gd0.01Er0.01Ho0.01)Σ1.04(Ti0.97Nb0.04)Σ1.01Si8.06O25.21F0.90H6.42, Z = 4. The simplified formula is (Na,□)(K,Сs)(Ca,Pb,Sr,Na)SrLn3+Ti(Si8O21)OF(H2O)3, where Ce is the dominant lanthanoid. The crystal structure was solved by direct methods and refined to an R1 index of 2.74%. In kalyuzhnyite-(Ce), the main structural units are a heteropolyhedral Na–Sr–Ce–Ti sheet, ideally [NaSrCeTiOF]7+, and a double (Si8O21)10– sheet parallel to (010). In the Si–O sheet, the Si tetrahedra form ten-membered rings. This is the first occurrence of such a double Si–O sheet in a mineral. The two sheets connect via common vertices of Na-, Sr-, Ce- and Ti-polyhedra and SiO4 tetrahedra to form a framework. The interstitial cations and H2O groups, ideally [(CaK)(H2O)3]3+, occur within the Si–O sheet. The mineral is named in honour of Vasily Avksentievich Kalyuzhny (1899–1993) in recognition of his contributions to the geology of ore deposits of Komi Republic (USSR) and the mineralogy of granitic pegmatites (Tajikistan).

Letnikovite-(Ce), ideally (Na□)Ca2Ce2[Si7O17(OH)]F4(H2O)4, is a new mineral with no natural or synthetic analogues (IMA2022–132). The mineral occurs at the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan, in a silexite-like peralkaline pegmatite. Letnikovite-(Ce) occurs as isolated prismatic grains up to 0.03 × 0.1 mm in a quartz–pectolite aggregate. Associated minerals are quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite. The mineral is colourless with a vitreous lustre and a white streak, and Dcalc. is 2.847 g/cm3. Letnikovite-(Ce) is monoclinic, C2/m, a = 7.4726(3), b = 22.9196(9), c = 13.9360(6) Å, β = 105.550(5)° and V = 2299.43(17) Å3. The chemical composition of letnikovite-(Ce) is SiO2 42.38, Gd2O3 0.16, Eu2O3 0.28, Sm2O3 0.07, Nd2O3 5.64, Pr2O3 1.69, Ce2O3 11.73, La2O3 2.24, PbO 1.22, SrO 5.77, FeO 0.32, CaO 11.87, MgO 1.14, Cs2O 0.57, K2O 0.65, Na2O 2.24, H2O 7.79, F 7.29, O = F –3.07, total 99.98 wt.%. The empirical formula calculated on 7 Si apfu is Na0.72K0.14Cs0.04Ca2.10Sr0.55Mg0.28Pb0.05Fe0.04(Ce0.71Nd0.33La0.14Pr0.10Eu0.02Gd0.01)Σ1.31Si7O21.84F3.81H8.58 for Z = 4. The structural formula is (Na0.72Ca0.16□1.12)Σ2(Cs0.04□0.96)Σ1(Ca1.83□0.17)Σ2(Mg0.28Fe0.04□0.68)Σ1(Ln3+1.31Sr0.55Ca0.09Pb0.05)Σ2[Si7O17(OH)]F3.81(H2O)3.79, where Ln3+1.31 = (Ce0.71Nd0.33La0.14Pr0.10Eu0.02Gd0.01)Σ1.31. The simplified formula is (Na,□)2Ca2(Ln3+,Sr)2[Si7O17(OH)]F4(H2O)4, where Ce is the dominant lanthanoid. The crystal structure was solved by direct methods and refined to an R1 index of 4.2%. In letnikovite-(Ce), the main structural unit is a layer which consists of the central heteropolyhedral Ca–Ce sheet and two adjacent single [Si7O17(OH)] sheets parallel to (001). In the Si–O–OH sheet, the Si tetrahedra form five-membered and ten-membered rings. This is the first occurrence of a single [Si7O17(OH)]7– sheet in a mineral. The layers connect via Na and Cs at the interstitial A(1,2) sites, H2O groups and hydrogen bonding. The mineral is named in honour of Felix Artem'evich Letnikov (born October 3rd,1934) in recognition of his outstanding contributions to the field of petrology and geochemistry of Precambrian rocks.

Potassic-jeanlouisite, ideally K(NaCa)(Mg4Ti)Si8O22O2, is the first characterised species of oxo amphibole related to the sodium–calcium group, and derives from potassic richterite via the coupled exchange CMg–1W${\rm OH}_{{\rm \ndash 2}}^{\ndash}{} ^{\rm C}{\rm Ti}_1^{{\rm 4 +}} {} ^{\rm W}\!{\rm O}_2^{2\ndash} $. The mineral and the mineral name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2018-050. Potassic-jeanlouisite was found in a specimen of leucite which is found in the lava layers, collected in the active gravel quarry on Zirkle Mesa, Leucite Hills, Wyoming, USA. It occurs as pale yellow to colourless acicular crystals in small vugs. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: A(K0.84Na0.16)Σ1.00B(Ca0.93Na1.02Mg0.04${\rm Mn}_{{\rm 0}{\rm. 01}}^{2 +} $)Σ2.00C(Mg3.85${\rm Fe}_{{\rm 0}{\rm. 16}}^{2 +} $Ni0.01${\rm Fe}_{{\rm 0}{\rm. 33}}^{3 +} {\rm V}_{{\rm 0}{\rm. 01}}^{3 +} $Ti0.65)Σ5.01T(Si7.76Al0.09Ti0.15)Σ8.00O22W[O1.53F0.47]Σ2.00. The holotype crystal is biaxial (–), with α = 1.674(2), β = 1.688(2), γ = 1.698(2), 2Vmeas. = 79(1)° and 2Vcalc. = 79.8°. The unit-cell parameters are a = 9.9372(10), b = 18.010(2), c = 5.2808(5) Å, β = 104.955(2)°, V = 913.1(2) Å3, Z = 2 and space group C2/m. The strongest eight reflections in the powder X-ray pattern [d values (in Å) (I) (hkl)] are: 2.703 (100) (151); 3.380 (87) (131); 2.541 (80) ($\bar 2$02); 3.151 (70) (310); 3.284 (68) (240); 8.472 (59) (110); 2.587 (52) (061); 2.945 (50) (221,$\bar 1$51).

Natrotitanite, ideally (Na0.5Y0.5)Ti(SiO4)O, is a new mineral from the Verkhnee Espe rare-element deposit at the northern exo-contact of the Akjailyautas granite massif in the northern part of the Tarbagatai mountain range, Eastern Kazakhstan. Both the mineral and the name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2010-033). Star-shaped aggregates of small short prisms of yellow or yellowish white (Na,Y,REE)-bearing titanite rimmed by thin (∼2 μm) rims of natrotitanite are embedded in yttrium-bearing fluorite and replace narsarsukite. Associated minerals are microcline, albite, quartz, riebeckite, aegirine, biotite, astrophyllite, rutile, zircon and elpidite. Natrotitanite is milky white to yellowish grey, transparent to translucent, and has a white streak and a vitreous lustre. It shows pale orange cathodoluminescence but does not fluoresce under ultraviolet light. It shows no cleavage or parting, and is brittle; the calculated density is 3.833 g cm–3. The indices of refraction, measured with the Bloss spindle stage for the wavelength 590 nm using a gel filter, are α = 1.904, γ = 2.030, and these values are in accord with the mean refractive index, 1.988, calculated from the Gladstone-Dale relation. Natrotitanite is monoclinic, C2/c, a = 6.5691(2), b = 8.6869(3), c = 7.0924(2) Å, β = 114.1269(4)°, V = 369.4(2) Å3, Z = 4, a:b:c = 0.7562:1: 0.8164. The seven strongest lines in the X-ray powder diffraction pattern [in the order d (Å), I, (hkl)] are as follows: 2.597, 10, (130); 3.248, 8, (11); 2.994, 6, (200); 1.641, 4, (330); 4.941, 3, (110); 1.498, 3, (400); 2.273, 3, (11). Chemical analysis by electron microprobe gave Nb2O5 1.28, SiO2 27.83, TiO2 35.00, SnO2 0.57, V2O3 0.36, Fe2O3 0.23, Y2O3 7.87, Ce2O3 0.83, Sm2O3 0.26, Gd2O3 0.46, Tb2O3 0.17, Dy2O3 2.45, Ho2O3 0.16, Er2O3 2.24, Tm2O3 0.50, Yb2O3 2.53, Nd2O3 0.35, Lu2O3 0.28, MnO 0.33, CaO 8.16, Na2O 5.55, F 1.52 O ≡ F –0.64, sum 98.71 wt.%. The resulting empirical formula is (Na0.39Ca0.32Y0.15Dy0.03Yb0.03Er0.03Ce0.01Ho0.01Tm0.01Gd0.01Nd0.01)Σ1.00(Ti0.95Nb0.02Sn0.01Fe3+0.01Mn0.01V0.01)Σ1.01Si1.01O4.00(O0.83F0.17), calculated on the basis of 3 cations per formula unit. The general formula is written as (Na,Ca,Y,REE)TiSiO4(O,F), and the endmember formula is (Na0.5Y0.5)Ti(SiO4)O.

The crystal structure of a composite optically continuous crystal of natrotitanite and (Na, Y)-bearing titanite was mounted on a Bruker D8 three-circle diffractometer equipped with a rotating anode generator (MoKα radiation), a multi-layer optics incident-beam path and an APEX-II CCD detector. The crystal structure was refined in space group C2/c to a final R1 index of 1.8%. Natrotitanite is isostructural with titanite, (Na + Y + REE) replacing Ca at the Ca site in the titanite structure.

The crystal structures of twenty-five orthorhombic Fe-Mg-Mn amphiboles, a = 18.525 – 18.620, b = 17.806-18.034, c = 5.264-5.303 Å, V = 1737.6-1776.7, space group = Pnma, Z = 4, have been refined to R indices in the range 2.1–7.8% using 790–1804 unique observed reflections measured with Mo-Kα X-radiation on a Bruker P4 automated four-circle diffractometer equipped with a 1K CCD detector. The quality of the refinements is strongly a function of the [4]Al content of the crystals because of unmixing in the central part of the series due to the presence of a low-temperature solvus. The amphibole crystals were analysed by electron microprobe subsequent to collection of the X-ray intensity data and span the anthophyllite-gedrite series from 0.17–1.82 [4]Al a.p.f.u. Mössbauer spectroscopy shows that the amphiboles of this series commonly contain small but significant amounts of Fe3+ . The amount of [4]Al is linearly related to the grand <T-O> distance by the equation <T-O> = 1.6214 + 0.171 [4]Al, R = 0.980; the slope of this relation is not significantly different from that characteristic of a hard-sphere model. The <T-O> distances indicate the following site preference for [4]Al: T1B > T2B > T1A » T2A. The <M2-O> distances are compatible with all [6]Al and Fe3+ ordered at the M2 site. The grand <M1,2,3 '3 –O> distance is related to the mean radius of the constituent cations, <rM1,2,3>, by the equation ≪M1,2,3-O≫ = 1.4684 + 0.8553(7) <rM1,2,3>.

The crystal structure of kraisslite, orthorhombic (pseudo-hexagonal), a = 8.1821(1), b = 14.1946(3), c = 43.9103(8) Å, V = 5099.8(2) Å3, Z = 4 and d calc = 4.083 g cm–3, has been solved bydirect methods and refined in the space group C2221 to an R 1 index of 1.68% for 7432 observed (|F o| > 4σ|F|) reflections. Electron-microprobe analysis gave the following chemical composition: As2O510.86,As2O36.18, SiO213.39, Al2O30.25, Fe2O32.06, MnO 51.14, ZnO 7.39, MgO 2.13, CaO 0.05, H2Ocalc = 4.50, sum 97.95 wt.%; and empirical formula: Zn2.91(Mn23.07Mg1.69Ca0.03)Σ=24.79(Fe0.83 3+Al0.16)Σ=0.99(As3+O3)2[(Si0.71As0.30 5+)O4]10(OH)16 calculated on the basis of 62 anions with (OH) = 16 and As3+/(As3++ As5+) taken from the refined crystal structure. The general formula, [4]Zn3(Mn,Mg)25(Fe3+,Al)(As3+O3)2[(Si,As5+)O4]10(OH)16, differs from those given previously.

There is one As3+ site with a <As–O> distance of 1.780 Å and a stereochemistry typical of a stereoactive lone-pair of electrons. There are five tetrahedrally coordinated T sites with <T–O> distances from 1.635 to 1.692 Å; the T(1)site is fully occupied by As5+, and the T(2)–T(5) sites are occupied by both Si and As5+. There are two tetrahedrally coordinated Zn sites with <T–O> distances of ∼1.996 Å, both of which are occupied by dominantZn and minor Mn2+. There are thirteen octahedrally coordinated M sites, twelve of which are occupied by dominant Mn2+ with lesser Mg and minor Zn; <M–O> distances are in the range 2.197–2.284 Å. The <M(13)–O> distanceis 2.083 Å and its lower site scattering indicates occupancy by Fe3+, Mn2+, Mg and Al. The structure consists of five crystallographically distinct layers of polyhedra, labelled m = 0 – 4. Layer m = 0 consists of corner-sharing Zn and (Si, As5+)tetrahedra, and layers m = 1–4 each consist of trimers of Mn2+ octahedra linked by (Si, As5+) tetrahedra and intrasheet hydrogen bonds (m = 1, 3) or (Si, As5+) tetrahedra and (Fe3+,Al) octahedra (m = 2) or (As5+)tetrahedra and (As3+O3) triangular pyramids and intrasheet hydrogen bonds (m = 4). The layers stack along [001] with reversals of the sequence m = 1, 2, 3, 4 at z = 0, ¼, ½ and ¾. Kraisslite is a member of the mcgovernite family.

The crystal structure of zoned philipsbornite – hidalgoite, hexagonal (rhombohedral), Rm , Z = 3: a = 7.1142(4), c = 17.0973(9) A ˚ , V = 749.4(1) Å3, from the Tsumeb mine, Namibia, has been refined to R1 = 1.68% for 301 unique reflections collected on a Bruker D8 three-circle diffractometer equipped with a rotating-anode generator, multilayer optics and an APEX-II CCD detector. Chemical analysis by electron microprobe showed zoned crystals with a rim enriched in S and Fe relative to the core. The core composition is SO3 3.31, As2O5 30.57, Al2O3 23.05, FeO 1.44, PbO 33.94, H2Ocalc 9.58, total 101.79 wt.%, corresponding to Pb0.982+(Al2.92Fe0.132+)(AsO4)[(As0.72S0.27)O3.14(OH)0.85](OH)6; and the rim composition is SO3 8.88, As2O5 22.63, Al2O3 22.90, FeO 2.57, PbO 34.91, H2Ocalc 9.27, total 101.16 wt.%, corresponding to Pb0.992+(Al2.85Fe0.232+)(AsO4)[(As0.25S0.70)O3.30(OH)0.50](OH)6. Philipsbornite – hidalgoite has the alunite-type structure, sheets of corner-sharing octahedra, decorated on top and bottom by [(As,S)O4] and (AsO3OH) tetrahedra, that are linked into a three-dimensional structure by [12]-coordinated Pb2+ cations and hydrogen bonds. A new hydrogen-bonding scheme for the D2+G33+(T5+O4)(TO3OH)(OH)6 minerals is proposed.

Fluoroleakeite, NaNa2(Mg2Fe3+2Li)Si8O22F2 is a new mineral of the amphibole group from the Verkhnee Espe deposit, Akjailyautas mountains, eastern Kazakhstan district, Kazakhstan. The granites and their host rocks have been intensely reworked by post-magmatic and host-rock fluids, resulting in intense recrystallization, enrichment in F, Li and rare elements, and replacement of primary biotite and sodic-calcic amphiboles by Li-bearing riebeckite, aegirine, astrophyllite and other sodic minerals including fluoroleakeite. Crystals are prismatic parallel to [001] with {100} and {110} faces and cleavage surfaces, and the prism direction is terminated by irregular fractures. Grains are up to 3 mm long, and occur as isolated crystals, as small aggregates, and as inclusions in cámaraite. Crystals are black with a very pale grey to colourless streak. Fluoroleakeite is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage, no observable parting, and has a calculated density of 3.245 g cm–3. In plane-polarized light, it is pleochroic, X = pale grey-green, Y = medium grey, Z = grey-brown; X^a = 14.1° (in β obtuse), Y ‖ b, Z^c = 75.9° (in β acute). Fluoroleakeite is biaxial negative, α = 1.663(2), β = 1.673(2), γ = 1.680(2); 2Vobs = 80.9(6)°, 2Vcalc = 79.4°

Fluoro-leakeite is monoclinic, space group C2/m, a = 9.8927(3), b = 17.9257(6), c = 5.2969(2) Å, β = 103.990(1)°, V = 905.7(1) Å3, Z = 2. The strongest ten X-ray diffraction lines in the powder pattern are [d in Å(I)(hkl)]: 2.718(100)(151), 8.434(40)(110), 4.464(30)(021), 3.405(30)(131), 3.137(20)(310), 2.541(20)(), 2.166(20)(261), 2.325(15)(), 2.275(15)() and 2.806(10)(330). Analysis by a combination of electron microprobe and crystal-structure refinement gives SiO2 53.34, Al2O3 0.62, TiO2 1.27, V2O3 0.05, Fe2O3 15.10, FeO 6.00, MnO 2.04, ZnO 0.18, MgO 6.40, CaO 0.13, Na2O 9.08, K2O 1.98, Li2O 1.10, F 3.33, H2Ocalc 0.16, sum 99.39 wt.%. The formula unit, calculated on the basis of 23 O, is A(Na0.64K0.38)(Na1.98Ca0.02)(Li0.66Mg1.42Fe0.752+Mn0.262+Zn0.02Fe1.693+V0.013+Ti0.144+Al0.03) (Si7.93Al0.07)O22(F1.57OH0.16O0.27). Crystal-structure refinement shows Li to be completely ordered at the M(3) site. Fluoroleakeite, ideally NaNa2(Mg2Fe23+Li)Si8O22F2, is related to end-member leakeite, NaNa2(Mg2Fe23+Li)Si8O22(OH)2 by the substitution F → (OH).

Fluoro-potassic-pargasite, ideally AKBCa2C(Mg4Al) (Si6Al2)O22WF2, a new amphibole species, has been found in a skarn in the Tranomaro area, Madgascar. The sample used for the description of the new mineral species is a large single amphibole crystal, 4 mm × 2 mm × 2 cm in size, brownish-black with brownish-yellow phlogopite lamellae adhering to one face of the crystal. Fluoro-potassic-pargasite is brittle, has a Mohs hardness of 6.5 and a splintery fracture; it is non-fluorescent, has perfect {110} cleavage, no observable parting, and has measured and calculated densities of 3.46 and 3.151 g cm−3, respectively. In plane-polarized light, it is pleochroic, X = colourless to very pale grey, Y = very pale grey, Z = colourless; X ^ a = 46.9° (in β obtuse), Y ‖ b, Z ^ c = 31.4° (in β acute). It is biaxial positive, α = 1.638(2), β = 1.641(2), γ = 1.653(2); 2Vobs = 49.6(4)°, 2Vcalc = 53.4°.

Fluoro-potassic-pargasite is monoclinic, space group C2/m, a = 9.9104(2), b = 17.9739(4), c = 5.3205(1) Å, β = 105.534(2)°, V = 913.11(6) Å3, Z = 2. The eight strongest lines in the X-ray powder-diffraction pattern are [d in Å(I)(hkl)]: 3.133(100)(310), 3.270(55)(240), 2.809(47)(330). 8.413(45)(110), 2.698(39)(151), 3.374(31)(131), 2.934(29)(221) and 1.647(29)(461). Electron microp-robe analysis gives SiO2 40.20, Al2O3 17.61, TiO2 0.46, FeO 1.96, Fe2O3 2.51, MgO 16.95, MnO 0.05, CaO 13.18, Na2O 0.99, K2O 3.72, F 2.75, H2Ocalc 0.77, sum 99.99 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F) with (OH + F) = 2 - (2 × Ti), is A(K0.69Na0.28Ca0.04)∑=1.01BCa2.00C(Mg3.64Fe0.242+Mn0.01Al0.79Fe0.273+Ti0.05)∑=5.00T(Si5.80Al2.20)∑=8.00O22W[F1.26(OH)0.74]∑=2.00. The mineral species and name have been approved by the IMA CMNMC (IMA 2009-091).

Veblenite, ideally K2☐2Na(Fe2+5Fe3+4Mn2+7☐)Nb3Ti(Si2O7)2(Si8O22)2O6(OH)10(H2O)3, is a new mineral with no natural or synthetic analogues. The mineral occurs at Ten Mile Lake, Seal Lake area, Newfoundland and Labrador (Canada), in a band of paragneiss consisting chiefly of albite and arfvedsonite. Veblenite occurs as red brown single laths and fibres included in feldspar. Associated minerals are niobophyllite, albite, arfvedsonite, aegirine-augite, barylite, eudidymite, neptunite, Mn-rich pectolite, pyrochlore, sphalerite and galena. Veblenite has perfect cleavage on {001} and splintery fracture. Its calculated density is 3.046 g cm–3. Veblenite is biaxial negative with α 1.676(2), β 1.688(2), γ 1.692(2) (λ 590 nm), 2Vmeas = 65(1)°, 2Vcalc = 59.6°, with no discernible dispersion. It is pleochroic in the following pattern: X = black, Y = black, Z = orange-brown. The mineral is red-brown with a vitreous, translucent lustre and very pale brown streak. It does not fluoresce under short and long-wave UV-light. Veblenite is triclicnic, space group P, a 5.3761(3), b 27.5062(11), c 18.6972(9) Å, α 140.301(3), β 93.033(3), γ 95.664(3)°, V = 1720.96(14) Å3. The strongest lines in the X-ray powder diffraction pattern [d(Å)(I)(hkl)] are: 16.894(100)(010), 18.204(23)(01), 4.271(9)(, 040, 120), 11.661(8)(001), 2.721(3)(), 4.404(3)(, ), 4.056(3)(031, 12; , ), 3.891(2)(003).

The chemical composition of veblenite from a combination of electron microprobe analysis and structural determination for H2O and the Fe2+/Fe3+ ratio is Nb2O5 11.69, TiO2 2.26, SiO2 35.71, Al2O3 0.60, Fe2O3 10.40, FeO 11.58, MnO 12.84, ZnO 0.36, MgO 0.08, BaO 1.31, SrO 0.09, CaO 1.49, Cs2O 0.30, K2O 1.78, Na2O 0.68, H2O 4.39, F 0.22, O = F –0.09, sum 95.69 wt.%. The empirical formula [based on 20 (Al+Si) p. f. u. is (K0.53Ba0.28Sr0.03☐0.16)Σ1(K0.72Cs0.07☐1.21)Σ2(Na0.72Ca0.17☐1.11)Σ2(Fe2+5.32Fe3+4.13Mn2+5.97Ca0.70Zn0.15Mg0.07☐0.66)Σ17(Nb2.90Ti0.93Fe3+0.17)Σ4(Si19.61Al0.39)Σ20O77.01H16.08F0.38. The simplified formula is (K, Ba, ☐)3(☐, Na)2(Fe2+, Fe3+, Mn2+)17(Nb,Ti)4(Si2O7)2(Si8O22)2O6(OH)10(H2O)3. The infrared spectrum of the mineral contains the following bands (cm–1): 453, 531, 550, 654 and 958, with shoulders at 1070, 1031 and 908. A broad absorption was observed between ~3610 and 3300 with a maximum at ~3525. The crystal structure was solved by direct methods and refined to an R1 index of 9.1%. In veblenite, the main structural unit is an HOH layer, which consists of the octahedral (O) and two heteropolyhedral (H) sheets. The H sheet is composed of Si2O7 groups, veblenite Si8O22 ribbons and Nb-dominant D octahedra. This is the first occurrence of an eight-membered Si8O22 ribbon in a mineral crystal structure. In the O sheet, (Fe2+, Fe3+, Mn2+) octahedra share common edges to form a modulated O sheet parallel to (001). HOH layers connect via common vertices of D octahedra and cations at the interstitial A(1,2) and B sites. In the intermediate space between two adjacent HOH layers, the A(1) site is occupied mainly by K; the A(2) site is partly occupied by K and H2O groups, the B site is partly occupied by Na. The crystal structure of veblenite is related to several HOH structures: jinshanjiangite, niobophyllite (astrophyllite group) and nafertisite. The mineral is named in honour of David R. Veblen in recognition of his outstanding contributions to the fields of mineralogy and crystallography.

Fluoro-potassic-magnesio-arfvedsonite, ideally AKBNa2c(Mg4Fe3+)TSi8O22wF2, has been found in a dyke ∼25 km southwest of Monte Metocha, Xixano region, northeastern Mozambique. Fluoro-potassic-magnesio-arfvedsonite and low sanidine form a fine-grained mafic, ultrapotassic, peralkaline igneous rock without visible phenocrysts. The amphibole is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage and no observable parting, and has a calculated density of 3.174 gcm−3. In plane-polarized light, it is pleochroic, X= pale grey-green, Y = blue-green, Z = pale grey; X ^ c = 23.6° (in β obtuse), Y ‖ b, Z ^ c = 66.4° (in β acute). Fluoro-potassic-magnesio-arfvedsonite is biaxial negative, α = 1.652(2), β = 1.658(2), γ = 1.660(2); 2Vobs = 22.5(7)°, 2Vcalc = 30.2°. The unit-cell dimensions are a = 9.9591(4), b = 17.9529(7), c = 5.2867(2) Å, β = 104.340(1)°, V = 919.73(10) Å3, Z = 2. The nine strongest X-ray diffraction lines in the experimental powder pattern are: [d in Å(I)(hkl)]: 2.716(100)(151), 3.410(70)(131), 8.475(50)(110), 3.178(50)(310), 3.309(30)(240), 2.762(20)(31), 2.549(20)(260), 2.351(10)(51), 2.269(10)(331). Electron microprobe analysis gave: SiO2 54.25, A12O3 0.03, TiO2 1.08, FeO 6.69, Fe2O3 8.07, MgO 13.99, MnO 0.32, ZnO 0.05, CaO 1.16, Na2O 6.33, K2O 5.20, F 2.20, H2Ocalc 0.74, sum 99.18 wt.%. The formula unit, calculated on the basis of 24 (O,OH,F) with (OH+F) = 2−(2 Ti), is AKa0.98B(Na1.18Ca0.18)∑1.99C(Mg3.07Fe0.832+Mn0.04Al0.01Fe0.903+Ti0.12Zn0.01)∑=4.98TSi8O22W[Fi.o3(OH)0.73O0.24]∑2.00 and confirms the usual pattern of cation order in the amphibole structure. The presence of a significant oxo component (locally balanced by Ti at the M(1) site) is related to the crystallization conditions. The presence of Fe3+ at the T sites, originally suggested for the holotype specimen, is discounted for this amphibole composition.

Tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, shows a variety of habits that resemble mushrooms, and it is commonly referred to as ‘mushroom tourmaline'. The structure of nine single crystals of elbaite, ranging in colour from pink to white to black and purple, extracted from two samples of mushroom tourmaline from Mogok, have been refined (SREF) to R indices of ~2.5% using graphite-monochromated Mo-Kα X-radiation. 11B and 27Al Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy shows the presence of [4]B and the absence of [4]Al in samples with transition-metal content low enough to prevent paramagnetic quenching of the signal. Site populations were assigned from refined site-scattering values and unit formulae derived from electron-microprobe analyses of the crystals used for X-ray data collection. 57Fe Mössbauer spectroscopy shows that both Fe2+ and Fe3+ are present, and the site populations derived by structure refinement show that there is no Fe at the Z site; hence all Fe2+ and Fe3+ occurs at the Y site. The 57Fe Mössbauer spectra also show peaks due to intervalence charge-transfer involving Fe2+ and Fe3+ at adjacent Y sites. Calculation of the probability of the total amount of Fe occurring as Fe2+–Fe3+ pairs for a random short-range distribution is in close accord with the observed amount of Fe involved in Fe2+–Fe3+, indicating that there is no short-range order involving Fe2+ and Fe3+ in these tourmalines.

Ferri-fluoro-katophorite is the second species characterised involving the rootname katophorite in the sodium–calcium subgroup of the amphibole supergroup. The mineral and its name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2015-096. It was found in the Bear Lake diggings, Bancroft area, Ontario, Canada, where coarse euhedral crystals of amphibole, phlogopite, sanidine solid-solution (now coarsely exsolved to microcline perthite), titanite, augite, zircon and fluorapatite crystallised from a low-viscosity silicocarbonatitic magma of crustal origin. Greenish grey prismatic crystals of ferri-fluoro-katophorite generally protrude from the walls into a body of coarsely crystalline calcite, but they also occur away from the walls, completely enclosed by calcite. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: A(Na0.55K0.32)Σ0.87B(Na0.79Ca1.18Mn2+0.03)Σ2.00C(Mg3.29Mn2+0.02Fe2+1.19Fe3+0.31Al0.09Ti4+0.08Li0.02)Σ5.00T(Si7.39Al0.61)Σ8.00O22W[F1.23 (OH)0.77]Σ2.00. Ferri-fluoro-katophorite is biaxial (–), with α = 1.640(2), β = 1.652(2), γ = 1.658(2), 2Vmeas. = 68.9(2)° and 2Vcalc.. = 70.1°. The unit-cell parameters are a = 9.887(3), b = 18.023(9), c = 5.292(2) Å, β = 104.66(3)°, V = 912.3(6) Å3, Z = 2 and space group C2/m. The strongest ten lines in the powder X-ray pattern [d values (in Å) I (hkl)] are: 2.708, 100, (151); 2.388, 74, (131); 3.139, 72, (310); 8.449, 69, (110); 2.540, 65, ($\bar{2}$02); 2.591, 53, (061); 2.739, 47, ($\bar{3}$31); 2.165, 45, (261); 3.279, 44, ($\bar{2}$40); 2.341, 43, ($\bar{3}$51).

Magnesio-hornblende (IMA2017-059) has been characterized in a specimen collected in the sand dunes of Lüderitz, Karas Region, Namibia. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is A(□0.73Na0.22K0.05)Σ1.00B(Ca1.79Fe2+0.10Mg0.04Mn2+0.03Na0.04)Σ2.00C(Mg3.48Fe2+0.97Al0.28Fe3+0.23Cr3+0.01Ti0.03)Σ5.00T(Si7.18Al0.82)Σ8.00O22W[(OH)1.93F0.05Cl0.02]Σ2.00. Magnesio-hornblende is biaxial (–), with α = 1.640(2), β = 1.654(2), γ = 1.666(2) (measured with gel-filtered Na light, λ = 589.9 nm), 2V (meas.) = 82(1)° and 2V (calc.) = 84.9°. The unit-cell parameters are a = 9.8308(7), b = 18.0659(11), c = 5.2968(4) Å, β = 104.771(6)° and V = 909.64 (11) Å3 with Z = 2 and space group C2/m. The strongest eight reflections in the X-ray powder pattern [d values (in Å), I, (hkl)] are: 2.709, 100, (151); 8.412, 74, (110); 3.121, 73, (310); 2.541, 58, ($\bar{2}$02); 3.386, 49, (131); 2.596, 45, (061); 2.338, 41, ($\bar{3}$51); and 2.164, 39, (261).

The crystal structures of carlfrancisite, ideally Mn32+(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]8(OH)42, hexagonal (rhombohedral), R3̄m with Z = 6, and unit-cell parameters: a = 8.2238(2), c = 205.113(6) Å and V = 12013.5(4) Å3, from the Kombat mine, Otavi Valley, Namibia, and mcgovernite, ideally Zn3(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]8(OH)42, hexagonal (rhombohedral), R3̄m with Z = 6, and unit-cell parameters: a = 8.2061(3), c = 204.118(8) Å and V = 11903.8(6) Å3, from Sterling Hill, New Jersey, have been solved by direct methods and refined to R1 values of 3.37 and 5.02% for 3837 and 3772 unique observed reflections, respectively; they are isostructural. Chemical analysis by electron microprobe and crystal-structure refinement gave the following compositions: carlfrancisite: As2O5 12.89, As2O3 3.33, P2O5 0.50, V2O5 0.74, SiO2 8.96, Al2O3 0.78, FeO 0.22, MnO 53.25, MgO 9.37, H2O(calc) 8.42, sum 98.50 wt.%; mcgovernite: As2O5 13.06, As2O3 3.71, SiO2 9.34, Al2O3 0.20, FeO 1.38, MnO 44.58, ZnO 8.81, MgO 8.89, H2O(calc) 8.24, sum 98.21 wt.%. The H2O contents and the valence states of As were determined by crystal-structure analysis.

There are 18 crystallographically distinct cation sites in both carlfrancisite and mcgovernite. There are two [4]-coordinated As sites fully occupied by As5+, and four T sites occupied by Si and As5+ in solid solution. The As(3) site has triangular pyramidal coordination with <As(3)–O> distances of 1.808 and 1.817 Å, typical of As3+. The Z(1) site, occupied by Mn2+ in carlfrancisite and Zn in mcgovernite, has tetrahedral coordination, and the Z(2) site is only partly occupied by Mg and Mn2+ in both structures. There are nine M sites, all of which are octahedrally coordinated and contain dominantly Mn2+ and Mg, with minor Al and Fe. There are three cation sites with significant vacancies: As(3), Z(2), M(3), and there are complicated patterns of short-range order involving the cations and vacancies at these sites.

The carlfrancisite–mcgovernite structure contains 84 layers of approximately close-packed polyhedra along one translation on c. The anions in the structure are arranged in approximately close-packed layers orthogonal to the c axis. Fourteen layers stack along the c axis in the sequence |**hhchch•hchchh| (* denotes a layer of anions displaced from close packed). There are eight distinct layers of cation-centred polyhedra that repeat via a centre of symmetry at the origin, and via the R-centering to give 84 layers per unit-cell.

During systematic characterization of amphiboles that still lack a complete mineral description, fluoro-tremolite was identified in a specimen from the Limecrest-Southdown quarry, Sparta, New Jersey, USA, which was provided by the Franklin Mineral Museum. The ideal formula of fluoro-tremolite is A□ BCa2CMg5TSi8O22WF2 and the empirical formula derived for the holotype specimen, based on the results of electron-microprobe analysis and single-crystal structure refinement, is A(Na0.28K0.02)Σ0.30B(Ca1.99Na0.01)Σ2.00C(Mg4.70${\rm Fe}_{{\rm 0}{\rm. 28}}^{{\rm 2 +}} $Zn0.01${\rm Ti}_{{\rm 0}{\rm. 01}}^{{\rm 4 +}} $)Σ5.00T(Si7.68Al0.32)Σ8.00O22W(F1.16OH0.84)Σ2.00. The unit-cell dimensions in space group C2/m are a = 9.846(2), b = 18.050(3), c = 5.2769(14) Å, β = 104.80(2)° and V = 906.7 (3) Å3 and Z = 2; the a:b:c ratio is 0.545:1:0.292. Fluoro-tremolite is biaxial (+), with α = 1.5987(5), β = 1.6102(5), γ = 1.6257(5), 2V(meas.) = 85(1)o and 2V(calc.) = 82o. The strongest ten reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 2.706, 100, (151); 3.126, 67, (310); 2.531, 59, ($\bar 2$02); 3.381, 57, (131); 2.940, 43, ($\bar 1$51, 221); 3.276, 37, (240); 2.337, 36, ($\bar 3$51); 2.592, 35, (061); 2.731, 34, ($\bar 3$31); 2.163, 34, (261). Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2016–018); the holotype has been deposited at the Franklin Mineral Museum (32 Evans Street, Franklin, 07416 New Jersey, US), under the catalogue number 7710.

Comparison with new data on tremolite and synthetic fluoro-tremolite provides a more sound crystal-chemical model of the end-member compositions and their solid-solution.

Clino-suenoite, ideally □${\rm Mn}_{2}^{2 +} $Mg5Si8O22(OH)2 is a new amphibole of the magnesium-iron-manganese subgroup of the amphibole supergroup. The type specimen was found at the Lower Scerscen Glacier, Valmalenco, Sondrio, Italy, where it occurs in Mn-rich quartzite erratics containing braunite, rhodonite, spessartine, carbonates and various accessory minerals. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: ANa0.04B(${\rm Mn}_{1.58}^{2 +} $Ca0.26Na0.16)Σ2.00C(Mg4.21${\rm Mn}_{0. 61}^{2 +} {\rm Fe}_{0.04}^{2 +} $Zn0.01Ni0.01${\rm Fe}_{0.08}^{3 +} $Al0.04)Σ5.00TSi8.00O22W[(OH1.94F0.06)]Σ=2.00. Clino-suenoite is biaxial (+), with α = 1.632(2), β = 1.644(2), γ = 1.664(2) and 2Vmeas. = 78(2)° and 2Vcalc. = 76.3°. The unit-cell parameters in the C2/m space group are a = 9.6128(11), b = 18.073(2), c = 5.3073(6) Å, β = 102.825(2)° and V = 899.1(2) Å3 with Z = 2. The strongest ten reflections in the powder X-ray diffraction pattern [d (in Å), I, (hkl)] are: 2.728, 100, (151); 2.513, 77, ($\bar 2$02); 3.079, 62, (310); 8.321, 60, (110); 3.421, 54, (131); 2.603, 42, (061); 2.175, 42, (261); 3.253, 41, (240); 2.969, 40, (221); 9.036, 40, (020).

Odigitriaite, a new Cs, Na, Ca borosilicate mineral, was discovered in moraine adjacent to the Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river at the intersection of the Turkestansky, Zeravshansky and Alaisky mountain ridges, Tajikistan. It occurs as irregular thin flakes associated with quartz, pectolite, baratovite, fluorite, pekovite, polylithionite, aegirine, leucosphenite, pyrochlore, neptunite, reedmergnerite, mendeleevite-(Ce), zeravshanite and sokolovaite. It is colourless with a white streak, is translucent and has a vitreous lustre; it does not fluoresce under ultraviolet light. Odigitriaite is brittle with an uneven fracture and a Mohs hardness of 5. The calculated density is 2.80(2) g/cm3. The indices of refraction are α = 1.502, β = 1.564, γ = 1.576; 2Vobs = 46(2)°, dispersion is weak r > v, and there is no pleochroism. The chemical composition is as follows (electron microprobe, H2O calculated from structure): SiO2 55.30, Al2O3 0.09, Y2O3 0.44, MnO 0.94, FeO 0.10, PbO 0.21, K2O 0.01 Cs2O 8.36, B2O3 4.75, H2O 0.37, F 1.74, O = F2 –0.74, total 99.43 wt.%. The empirical formula of odigitriaite is Cs0.90Na5.12Ca4.68Mn0.20Y0.06Fe0.02Pb0.01[Si13.92Al0.03B2.06O38]F1.39(OH)0.62. The end-member formula is CsNa5Ca5[Si14B2O38]F2. The strong reflections in the powder X-ray diffraction pattern are: [(d, Å), (I, %), (hkl)]: 5.45 (25) (1 1 3), 4.66 (33) (3 1 1), 4.40 (26) (0 2 2), 4.10 (36) (3 1 3), 3.95 (25) (3̄ 1 3), 2.85 (31) (2 2 2), 2.68 (40) (0 0 6), 3.62 (45) (0 2 4), 3.35 (100) (2̄ 2 4), 3.31 (30) (3̄ 1 5), 3.25 (35) (4 0 4), 3.04 (60) (4̄ 2 2), 2.925 (22) (4̄ 2 3), 1.813 (23) (9 1 0). Odigitriaite is monoclinic, space group C2/c, a = 16.652(5), b = 9.598 (3), c = 22.120(7) Å, β= 92.875(14)°, V = 3530.9(1.9) Å3, Z = 4. The crystal structure of odigitriaite was solved by direct methods and refined to an R 1 value of 2.75% based on single-crystal X-ray data. It is a double-layer sheet-borosilicate mineral; Cs and Na are intercalated within the double-layer sheet, and the double layers are linked by interstitial Ca and Na atoms.