Wodegongjieite occurs in the Cr-11 chromitite orebody of the Luobusa ophiolite in the Kangjinla district, Tibet, China. It is found in two inclusions in corundum: (1) as a partial overgrowth (holotype) up to 1.5 μm thick around a spheroid 20 μm across of wenjiite (Ti10(Si,P,□)7), kangjinlaite (Ti11(Si,P)10), zhiqinite (TiSi2) and badengzhuite (TiP), and (2) as pools up to 0.25 μm wide filling interstices between wenjiite, jingsuiite (TiB2), osbornite–khamrabaevite (Ti[N,C]) and corundum. Energy dispersive analyses gave Al2O3 34.09, SiO2 49.11, K2O 2.56, CaO 11.71, SrO 2.53, total 100.0 wt.%, corresponding to K0.58Sr0.26Ca2.25Al7.20Si8.80O31.20, ideally KCa3(Al7Si9)O32, for Si + Al = 16 cations.

Single-crystal studies were carried out with three-dimensional electron diffraction providing data for an ab initio structure solution in the hexagonal space group P6/mcc (#192) with a = 10.2(2) Å, c = 14.9(3) Å, V = 1340(50) Å3 and Z = 2. Density (calc.) = 2.694 g⋅cm–3. The refinement, which assumes complete Si–Al disorder, gives average T1–O and T2–O bond lengths both as 1.65 Å. It was not practical to use unconstrained refinement for the occupancies of the large cation sites 6f and 2a. The ab initio model shows clearly that the two cation sites have different sizes and coordination. Consequently, we imposed the condition (1) that all the K occupies the 2a site as the average K–O bond length of 3.07 Å is close to the average K–O bond lengths reported in kokchetavite and (2) that all the Ca occupies the 6f site as the average Ca–O bond length of 2.60 Å (2.36 Å and 2.84 Å for Ca–O1 and Ca–O3, respectively) is reasonable for Ca–O. Assuming that all K and all Ca are located at the 2a site and 6f site, respectively, Sr occupancies of these sites could be refined. Thermal parameters are positive and in a reasonable range. The structure is a sheet silicate isostructural with the K-feldspar polymorph kokchetavite, with two crystallographically distinct sites for K, but not with the topologically identical anorthite polymorph dmisteinbergite (CaAl2Si2O8) with only a single site for Ca. Substitution of K by Ca at the 6f site is associated with marked rotation of the Si,Al tetrahedra and a collapse of the structure to accommodate the smaller Ca ion.

The spheroid of intermetallic phases is believed to have formed from the interaction of mantle-derived CH4 + H2 fluids with basaltic magmas at depths of ~30–100 km, resulting in precipitation of corundum that entrapped intermetallic melts. Associated immiscible silicate melt of granodioritic composition crystallised metastably to wodegongjieite instead of a mixture of anorthite and K-feldspar.

In 1884, Lorenzen proposed the formula MgAl2SiO6 for his new mineral kornerupine from Fiskenæsset and did not suspect it to contain boron. Lacroix and de Gramont (1919) reported boron in Fiskenæsset kornerupine, while Herd (1973) found none. New analyses (ion microprobe mass analyser and spectrophotometric) of kornerupine in three specimens from the type locality, including the specimens analysed by Lorenzen and Herd, indicate the presence of boron in all three, in amounts ranging from 0.50 to 1.44 wt.% B2O3, e.g. (Li0.04 Na0.01 Ca0.01) (Mg3.49 Mn0.01 Fe0.17 Ti0.01 Al5.64)Σ9.30 (Si3.67 Al1.02 B0.31)Σ5 O21 (OH0.99 F0.01) for Lorenzen's specimen. Textures and chemical compositions suggest that kornerupine crystallized in equilibrium in the following assemblages, all with anorthite (An 92–95) and phlogopite (XFe = atomic Fe/(Fe + Mg) = 0.028–0.035): (1) kornerupine (0.045)-gedrite (0.067); (2) kornerupine (0.038–0.050)-sapphirine (0.032–0.035); and (3) kornerupine (0.050)-hornblende. Fluorine contents of kornerupine range from 0.01 to 0.06%, of phlogopite, from 0.09 to 0.10%. In the first assemblage, sapphirine (0.040) and corundum are enclosed in radiating bundles of kornerupine; additionally sapphirine, corundum, and/or gedrite occur with chlorite and pinite (cordierite?) as breakdown products of kornerupine. Kornerupine may have formed by reactions such as: gedrite + sapphirine + corundum + B2O3 (in solution) + H2O = kornerupine + anorthite + Na-phlogopite under conditions of the granulite facies. Boron for kornerupine formation was most likely remobilized by hydrous fluids from metasedimentary rocks occurring along the upper contact of the Fiske⇒set gabbro-anorthosite complex with amphibolite.

Kornerupine and prismatine were introduced independently by Lorenzen in 1884 (but published in 1886 and 1893) and by Sauer in 1886, respectively. Ussing (1889) showed that the two minerals were sufficiently close crystallographically and chemically to be regarded as one species. However, recent analyses of boron using the ion microprobe and crystal structure refinement, indicate that the boron content of one tetrahedral site in kornerupine ranges from 0 to 1. Kornerupine and prismatine, from their respective type localities of Fiskenæsset, Greenland and Waldheim, Germany, are distinct minerals, members of an isomorphic series differing in boron content. For this reason, we re-introduce Sauer’s name prismatine for kornerupines with B > 0.5 atoms per formula unit (p.f.u.) of 22(O,OH,F), and restrict the name kornerupine sensu stricto to kornerupines with B < 0.5 p.f.u. Kornerupine sensu lato is an appropriate group name for kornerupine of unknown boron content. Kornerupine sensu stricto and prismatine from the type localities differ also in Fe2+/Mg ratio, Si − (Mg + Fe2+ + Mn) content, Al content, F content, colour, density, cell parameters, and paragenesis. Both minerals formed under granulite-facies conditions with sapphirine and phlogopite, but kornerupine sensu stricto is associated with anorthite and hornblende or gedrite, whereas prismatine is found with oligoclase (An9–13), sillimanite, garnet, and/or tourmaline. Occurrences at other localities suggest that increasing boron content extends the stability range of prismatine relative to that of kornerupine sensu stricto.

Högbomite, a complex oxide of A1, Fe, Mg, and Ti, is an important constitutent of some iron ores and emery deposits as well as an infrequent accessory in aluminous high-grade rocks (e.g. Grew et al., 1987). The recent increase in reports of new localities (e.g. Rammlmair et al.,1988) suggests that högbomite may be more widespread than is generally perceived. We report here högbomite from the Aldan Shield, Eastern Siberia. This högbomite is remarkable for the wide variation in composition measured in a single thin section. Our report is only the second from the USSR of högbomite for which chemical data are given.

In specimens of Mn skarn from the type locality of Långban, hyalotekite, (Ba,Pb,K)4Ca2−(Si,B,Be)12O28F, occurs in a matrix consisting mostly of aegirine (⩽22 mol.% CaMnSi2O6), andradite (⩽27 mol.% Mn3Fe2Si3O12), hematite, pectolite, quartz, calcite, baryte, barylite, and hedyphane. Melanotekite, plumbian taramellite, ferrian K-feldspar (to 6.5 wt.% Fe2O3), rhodonite, a talc-like mineral, apophyllite, and several Pb-As-Sb-O minerals are found in trace amounts. In a single specimen of reedmergnerite-microcline pegmatite from Dara-i-Pioz, hyalotekite occurs in close association with microcline. Other accessory minerals are albite, aegirine, pyrochlore, eudialyte, and polylithionite. The optical constants for hyalotekite from Långban and Dara-i-Pioz are, respectively, α = 1.656, 1.646, β = 1.659–1.660, 1.649, γ = 1.670–1.671, 1.659 (all ± 0.002), 2Vγ (mcas) = 57.2–60.5 ± 0.5°, 57.0 ± 1.1°(λ = 589 nm). Cell parameters of the Dara-i-Pioz hyalotekite for a body-centred triclinic cell are: a = 11.284(2), b = 10.930(1), c = 10.272(8) Å, α = 90.35(2)°, β = 90.11(3)°, γ = 89.98(1)°. Electron and ion microprobe data show that Långban hyalotekite is heterogeneous even within a given sample; the most important substitutions are Pb = Ba, K and coupled B = Si and B = Be. Minor constituents include Mn in the Långban hyalotekite and Na in the Dara-i-Pioz hyalotekite, which also differs in its significantly higher Ba/Pb ratio. Conditions suggested for hyalotekite formation at Långban and Dara-i-Pioz are P ⩽ 4 kbar, T ⩾ 500°C, silica saturation, peralkalinity, and relatively high oxygen fugacities and low sulphur fugacities. These temperatures must have been sufficiently high to allow for miscibility of Pb with Ba (and K) despite the lone pair of electrons of Pb2+.

The hyalotekite group has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (memorandum 57–SM/16). The general formula of the minerals of the hyalotekite group may be written as: A2B2M2[Si8T4O28]W where A = Ba2+, Pb2+ or K+; B = Ba2+, Pb2+ or K+; M = Ca2+, Y3+ or REE3+; T = Si4+, B3+ or Be2+; and W = F– or □ (where REE = rare-earth elements and □ = vacancy).

Four minerals are currently known in this group: hyalotekite, Ba4Ca2[Si8B2(SiB)O28]F, triclinic, I$\bar 1$; khvorovite, Pb2+4Ca2[Si8B2(SiB)O28]F, triclinic I$\bar 1$; kapitsaite-(Y), Ba4(YCa)[Si8B2B2O28]F, triclinic, I$\bar 1$; and itsiite Ba4Ca2[Si8B4O28]□, tetragonal, I$\bar 4$2m.

We explore the possible end-member compositions within this group by conflating the properties of an end-member with the stoichiometry imposed by the bond topology of the hyalotekite structure-type and the crystal-chemical properties of its known constituents. There are two high-coordination sites in the hyalotekite structure, A and B, and occupancy of each of these sites can be determined only by crystal-structure refinement. If these two sites are considered together, there are 19 end-member compositions of the triclinic structure and six end-member compositions of the tetragonal structure involving A and B = Ba2+, Pb2+, K+; M = Ca2+, Y3+, REE3+; and T = Si4+, B3+, Be2+. There is the possibility for many other hyalotekite-group minerals, and two potential new minerals have been identified from data in the literature.