Here we report a nomenclature and classification for the astrophyllite-supergroup minerals. The HOH block is the main structural unit in all astrophyllite-supergroup structures; it consists of three H–O–H sheets where the T4O12 astrophyllite ribbons occur in the H sheets. In each structure, HOH blocks alternate with I (Intermediate) blocks along [001]. The twelve minerals of the astrophyllite supergroup are divided into three groups based on (1) the type of self-linkage of HOH blocks, i.e. (a) HOH blocks link directly where they share common vertices of D octahedra, or (b) HOH blocks do not link directly; and (2) the dominant cation of the O sheet (the C group: C7 apfu). In the astrophyllite group (HOH blocks connect via D– XDP–D bridges, Fe2+ is dominant at C7), there are six minerals: astrophyllite, niobophyllite, zircophyllite, tarbagataite, nalivkinite and bulgakite. In the kupletskite group (HOH blocks connect via D–XDP–D bridges, Mn2+ is dominant at C7), there are three minerals: kupletskite, niobokupletskite and kupletskite-(Cs). In the devitoite group (HOH blocks do not connect via D–XDP–D bridges), there are three minerals: devitoite, sveinbergeite and lobanovite. The general formula for the astrophyllite-supergroup minerals is of the form A2pBrC7D2(T4O12)2IXD2OXA4OXDnPWA2, where C [cations at the M(1–4) sites in the O sheet] = Fe2+, Mn, Na, Mg, Zn, Fe3+, Ca, Zr, Li; D (cations in the H sheets) = [6,5]Ti, Nb, Zr, Sn4+ , [5]Fe3+, Mg, Al; T = Si, minor Al; A2pBrIWA2 (I block) where p = 1,2; r = 1,2; A = K, Cs, Ba, H2O, Li, Rb, Pb2+, Na,□; B = Na, Ca, Ba, H2O,□; I represents the composition of the central part of the I block, excluding peripheral layers of the form A2pBrWA2, e.g. (PO4)2(CO3) (devitoite); XDO = O; XAO = OH, F; XDP = F, O, OH, H2O,□, where n = 0, 1, 2 for (XDP)n; WA = H2O,□.

A gem-quality purplish-red tourmaline sample of alleged liddicoatitic composition from the Anjanabonoina pegmatite, Madagascar, has been fully characterised using a multi-analytical approach to define its crystal-chemical identity. Single-crystal X-ray diffraction, chemical and spectroscopic analysis resulted in the formula: X(Na0.41□0.35Ca0.24)Σ1.00Y(Al1.81Li1.00Fe3+0.04Mn3+0.02Mn2+0.12Ti0.004)Σ3.00ZAl6 [T(Si5.60B0.40)Σ6.00O18] (BO3)3 (OH)3W[(OH)0.50F0.13O0.37]Σ1.00 which corresponds to the tourmaline species elbaite having the typical space group R3m and relatively small unit-cell dimensions, a = 15.7935(4) Å, c = 7.0860(2) Å and V = 7.0860(2) Å3. Optical absorption spectroscopy showed that the purplish-red colour is caused by minor amounts of Mn3+ (Mn2O3 = 0.20 wt.%). Thermal treatment in air up to 750°C strongly intensified the colour of the sample due to the oxidation of all Mn2+ to Mn3+ (Mn2O3 up to 1.21 wt.%). Based on infrared and Raman data, a crystal-chemical model regarding the electrostatic interaction between the X cation and W anion, and involving the Y cations as well, is proposed to explain the absence or rarity of the mineral species ‘liddicoatite’.

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Lucchesiite, CaFe32+Al6(Si6O18)(BO3)3(OH)3O, is a new mineral of the tourmaline supergroup. It occurs in the Ratnapura District, Sri Lanka (6°35'N, 80°35'E), most probably from pegmatites and in Mirošov near Strážek, western Moravia, Czech Republic, (49°27'49.38"N, 16°9'54.34"E) in anatectic pegmatite contaminated by host calc-silicate rock. Crystals are black with a vitreous lustre, conchoidal fracture and grey streak. Lucchesiite has a Mohs hardnessof ∼7 and a calculated density of 3.209 g/cm3(Sri Lanka) to 3.243 g/cm3(Czech Republic). In plane-polarized light, lucchesiite is pleochroic (O = very dark brown and E = light brown) and uniaxial (–). Lucchesiite is rhombohedral, space groupR3m,a≈ 16.00 Å,c≈ 7.21 Å,V≈ 1599.9 Å3,Z= 3. The crystal structure of lucchesiite was refined toR1 ≈ 1.5% using ∼2000 unique reflections collected with MoKα X-ray intensity data. Crystal-chemical analysis for the Sri Lanka (holotype) and Czech Republic (cotype) samples resulted in the empirical formulae, respectively:X(Ca0.69Na0.30K0.02)∑1.01Y(Fe1.442+Mg0.72Al0.48Ti0.334+V0.023+Mn0.013+Zn0.01)∑3.00Z(Al4.74Mg1.01Fe0.253+)∑6.00[T(Si5.85Al0.15)∑6.00O18](BO3)3V(OH)3W[O0.69F0.24(OH)0.07]∑1.00andX(Ca0.49Na0.45□0.05K0.01)∑1.00Y(Fe1.142+Fe0.953+Mg0.42Al0.37Mn0.03Ti0.084+Zn0.01)∑3.00Z(Al5.11Fe0.383+Mg0.52)∑6.00[T(Si5.88Al0.12)∑6.00O18](BO3)3V[(OH)2.66O0.34]∑3.00W(O0.94F0.06)∑1.00.Lucchesiite is an oxy-species belonging to the calcic group of the tourmaline supergroup. The closest end-member composition of a valid tourmaline species is that of feruvite, to which lucchesiite is ideally related by the heterovalent coupled substitutionZAl3++O1O2–↔ZMg2++O1(OH)1–. The new mineral was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA 2015-043).