The LGC (Leinster Granite Complex) in SE Ireland consists of five plutons or Units. Units 1 and 3 display complex magmatic disequilibrium textures described here for the first time. The textures indicative of disequilibrium include boxy cellular plagioclase, oscillatory zoning, calcic spike zones and combinations of these within individual plagioclase feldspar crystals. The textures are interpreted as having formed in a dynamic magmatic environment which facilitated acid-acid mixing on a variety of scales and at a variety of stages between source to emplacement. It is proposed that the restricted distribution of disequilibrium textures was a result of the complex strain regime operating within the crust during assembly of Units 1 and 3.

In most documented occurrences, violarite (FeNi2S4) occurs as a product of the supergene alteration of primary pentlandite or millerite. Earlier experimental phase relations studies predicted the possible existence of a stable violarite–pentlandite tie line, though there has been little field evidence supporting this hypothesis, and the preferred topology in the Ni-Fe-S system involves a pyrite–millerite tie line. This paper documents the occurrence of violarite-pentlandite±pyrite assemblages which, on the basis of mineral chemistry and textural evidence, appear to be hypogene. Primary cobaltian violarite (with 2.1–13.2 wt.% Co) occurs as lamellae in pentlandite in the MKD5 nickel sulphide orebody at Mount Keith, central Western Australia. These lamellae are interpreted to be of exsolution origin. Cobalt is preferentially partitioned into violarite, resulting in high Ni:Co ratios in the associated pentlandite relative to pentlandite in violarite-free assemblages. Hypogene violarite-millerite±pentlandite assemblages were also noted. In all hypogene assemblages, violarite differs in both textural and mineral chemical characteristics from supergene violarite from the upper portions of the MKD5 orebody. The implications of the assemblages for the known low-temperature phase relations in the Ni-Fe-S-(Co) system are discussed.

We describe an ilmenite-bearing aplitic syenite dyke in the roof zone of the Tibchi granite, exposed at Kalato, in the Tibchi ring-complex, northern Nigeria. Inclusions of ferrocolumbite, rutile and ixiolite in the ilmenite are inferred to have been trapped at the magmatic stage. The main mafic mineral is annite. Compositionally, the ilmenite, rutile and ferrocolumbite have near-end-member compositions. A positive correlation between Sc and Ta/(Ta+Nb) indicates that Sc behaved incompatibly as ferrocolumbite grew. Such entrapped accessory minerals may well have formed by local saturation at the ilmenite-melt and annite-melt interface. During and after their crystallization, the melt reached saturation in H2O and degassed. A second generation of ilmenite enriched in Mn and Zn replaced the primary ilmenite along fractures and grain margins. As fO2 began to increase, composite blebs and rinds of ‘ferropseudobrookite’, rutile and hematite began to develop by oxidation-induced exsolution in the primary ilmenite. Incorporation of Nb, Ta, Sc and Si in the ‘ferropseudobrookite’ may well have stabilized it at Kalato. Ultimately, it is transformed to hematite + rutile. The IMA-sanctioned view that the solid solution between pseudobrookite and Ti3O5 is complete, and thus that ‘ferropseudobrookite’, as an intermediate member of the series, does not merit species status, needs to be re-evaluated.

Reaction textures including corona structures in granulites from the Proterozoic Long Range Inlier of western Newfoundland are spatially associated with a Silurian (0.34 Ga) mafic intrusion, the Taylor Brook Gabbro Complex. They comprise, in metabasites and tonalitic gneiss, coronal orthopyroxene and plagioclase on garnet and, in metapelites, cordierite and spinel formed at the expense of sillimanite, garnet and quartz. Although generally interpreted to indicate near-isothermal decompression (ITD) following regional metamorphism, which in the inlier occurred at ˜1.10–1.03 Ga, these features appear to be absent elsewhere. Therefore they are interpreted to be products of contact metamorphism (near-isobaric heating – IBH) within the thermal aureole of the gabbro. Thus, there is a ˜0.7 Ga difference (i.e. mid-Proterozoic vs. mid-Silurian) between the age of the regional metamorphic mineral assemblages and the contact aureole assemblages. The observation that classic ITD features occur in this aureole environment underscores the fact that P-sensitive reactions can progress during IBH as well as by pressure release.

Palladseite (palladium selenide) and palladian gold occur as euhedral inclusions in specularite and as infill of microfractures and interstices in magnetite aggregates (host rock fragments) within specularite-rich auriferous veins (jacutinga). Palladseite has minor amounts of Pt (0.6–3.5 wt.%), Cu (2.9–3.5 wt.%), Hg (0.9–1.9 wt.%), and Ag (0.3–0.5 wt.%). The palladian gold contains up to 6 wt.% Pd, and minor Cu and Ag. Isomertieite (Pd11Sb2As2) and sudovikovite (PtSe2) are also recorded. The veins cross-cut the main tectonic foliation of the wallrock (itabirite). The feature of fracture infill and the Se-Sb-As-Hg-Cu-Ag geochemical/mineralogical signature of the Au-Pd mineralization point to a post-ductile deformation and possibly low-temperature (epithermal) origin of the jacutinga mineralization style.

Palladseite is replaced locally by a Pd-rich oxidation phase. Electron microprobe analysis of alteration halos around palladseite yields 76–80 wt.% Pd. Oxygen calculated by stoichiometry accords with a monoxide compound of the type PdO. However, the measured oxygen content is lower than expected for the PdO stoichiometry, suggesting loss of volatile species, and a more ‘hydrated’ compound, such as an oxyhydroxide.

The new minerals manganvesuviante and tweddillite, both formed by hydrothermal alteration of primary manganese ores, are described from the Kalahari manganese fields (Republic of South Africa). In addition, single-crystal X-ray structure refinements of both new minerals are presented.

Manganvesuvianite is a tetragonal vesuvianite mineral with the simplified formula Ca19Mn3+(Al,Mn3+,Fe3+)10(Mg,Mn2+)2Si18O69(OH)9, characterized by Mn3+ occupying the five-coordinated position (square pyramid). The crystals simple prismatic forms: {100}, {110} terminated by {101} and exhibit deep maroon red colour. With polarized light the crystals are strongly pleochroic, yellowish parallel to E and dark red to lilac parallel to O.

Tweddillite is an epidote-group mineral (space group P21/m, a = 8.932(5), b = 5.698(4), c = 10.310(5) Å, β = 114.56(4), V = 477.3(8) Å3) with the simplified formula CaSr(Mn3+,Fe3+)2Al[Si3O12](OH), closely related to strontiopiemontite. The difference between strontiopiemontite and tweddillite is the concentration of octahedral Mn3+. Strontiopiemontite has Mn3+ mainly on the M3 site whereas tweddillite has Mn3+ with minor Fe3+ on M3 and M1. Tweddillite forms aggregates of very thin dark red {001} blades characterized by striking pleochroism. The crystals appear dark red parallel to b and orange-yellow parallel to a. Perpendicular to (001) the blades appear magenta to red.

Hoganite, copper(II) acetate monohydrate, and paceite (pronounced ‘pace-ite’), calcium(II) copper(II) tetraacetate hexahydrate, occur as isolated crystals embedded in ferruginous gossan from the Potosi Pit, Broken Hill, New South Wales, Australia. They are associated with goethite, hematite, quartz, linarite, malachite, azurite, cerussite and cuprian smithsonite. Hoganite is bluish green with a pale blue streak and a Mohs hardness of 1½; it possesses perfect {001} and distinct {110} cleavages and has a conchoidal fracture. Chemical analysis of hoganite gave (wt.%) C 23.85; H 3.95; Cu 31.6; Fe 0.4; O (by difference) 40.2, yielding an empirical formula of C4H7.89O5.07Cu1.00Fe0.01. The simplified formula is C4H8O5Cu or Cu(CH3COO)2.H2O, the mineral being identical to the synthetic compound of the same formula. Single-crystal X-ray data for hoganite are: monoclinic, space group C2/c, a = 13.162(3), b = 8.555(2), c = 13.850(3)Å, β = 117.08(3)°, Z = 8. The density, calculated from single-crystal data, is 1.910 g cm−3. The strongest lines in the X-ray powder pattern are [dobs (Iobs) (hkl)] 6.921 (100) (011); 3.532 (28) (202); 6.176 (14) (200); 3.592 (11) (22); 5.382 (10) (11); 2.278 (10) (204); 5.872 (9) (002). Hoganite (orientation presently unknown) is biaxial positive with α = 1.533(2), β = 1.541(3), γ = 1.554(2), 2V(meas.) = 85(5)°, 2V(calc.) = 76.8°, dispersion is r < v, medium (white light); it is strongly pleochroic with X = blue, Y = pale bluish, Z = pale bluish green and absorption X > Y > Z. The mineral is named after Graham P. Hogan of Broken Hill, New South Wales, Australia, a miner and well-known collector of Broken Hill minerals.

Paceite is dark blue with a pale blue streak and a Mohs hardness of 1½; it possesses perfect {100} and {110} cleavages and has an uneven fracture. Chemical analysis of paceite gave (wt.%) C 21.25; H 5.3; Ca 9.0; Cu 14.1; O (by difference) 50.35, yielding an empirical formula of C8H23.77O14.23Ca1.02-Cu1.00. The simplified formula is C8H24O14CaCu or CaCu(CH3COO)4.6H2O, the mineral being identical to the synthetic compound of the same formula. Unit-cell data (refined from X-ray powder diffraction data) for paceite are: tetragonal, space group I4/m, a = 11.155(4), c = 16.236(17)Å, Z = 4. The density, calculated from refined cell data, is 1.472 g cm−3. The strongest lines in the X-ray powder pattern are [dobs (Iobs) (hkl)] 7.896 (100) (110); 3.530 (20) (310); 5.586 (15) (200); 8.132 (8) (002); 9.297 (6) (101); 2.497 (4) (420); 3.042 (3) (321). Paceite is uniaxial positive with ω = 1.439(2) and ɛ = 1.482(3) (white light); pleochroism is bluish with a greenish tint (O), pale bluish with a greyish tint (E), and absorption O ⩾ E. The mineral is named after Frank L. Pace of Broken Hill, New South Wales, Australia, an ex-miner and well-known collector of Broken Hill minerals.

The importance of impact cratering on terrestrial planets is obvious from the abundance of craters on their surfaces. On Earth, active geological processes rapidly obliterate the cratering record. To date only about 170 impact structures have been recognized on the Earth's surface. Mineralogical, petrographic, and geochemical criteria are used to identify the impact origin of such structures or related ejecta layers. The two most important criteria are the presence of shock metamorphic effects in mineral and rock inclusions in breccias and melt rocks, as well as the demonstration, by geochemical techniques, that these rocks contain a minor extraterrestrial component. There is a variety of macroscopic and microscopic shock metamorphic effects. The most important ones include the presence of planar deformation features in rock-forming minerals, high-pressure polymorphs (e.g. of coesite and stishovite from quartz, or diamond from graphite), diaplectic glass, and rock and mineral melts. These features have been studied by traditional methods involving the petrographic microscope, and more recently with a variety of instrumental techniques, including transmission electron microscopy, Raman spectroscopy, cathodoluminescence imaging and spectroscopy, and high-resolution X-ray computed tomography. Geochemical methods to detect an extraterrestrial component include measurements of the concentrations of siderophile elements, mainly of the platinum-group elements (PGEs), and, more recently, chromium and osmium isotopic studies. The latter two methods can provide confirmation that these elements are actually of meteoritic origin. The Cr isotopic method is also capable of providing information on the meteorite type. In impact studies there is now a trend towards the use of interdisciplinary and multi-technique approaches to solve open questions.

Brinrobertsite, an ordered, mixed-layered, dioctahedral pyrophyllite-smectite (P/S), occurs in a metabentonite in the Ordovician Nant Ffrancon Formation near Bangor, N Wales. It comprises ~30% of the metabentonite, in association with quartz (~50%) and chlorite (clinochlore; 20%) which replaced glass shards and fine-grained glass matrix. Transmission electron microscopy (TEM) images show sequences of dominant ~24 Å 001 lattice fringes inferred to correspond to 2:1 layers with alternate pyrophyllite-like (low-charge) and smectite-like (higher-charge) interlayers (i.e. R1 ordering). The hk0 diffraction patterns are mostly hexanets with some spotty circles, implying that layers are largely coherently related, but with some turbostratic stacking. Collective data show that d100 = 5.2, b = 9.1, and d001 = 24–25 Å, assuming monoclinic or pseudomonoclinic symmetry. The composition, as determined by energy dispersive spectral analysis, is (Na0.22K0.07Ca0.06)(Al3.81Mg0.08Fe0.08)(Si7.84 Al0.16)O20(OH)4·3.54H2O, as consistent with the sum of the compositions of pyrophyllite-like and smectite-like units. Water content was determined by DTA/TGA analysis. The powder diffraction patterns have a principal peak with d001 = 24.4 Å. Patterns of air-dried and glycol-saturated brinrobertsite, including Na- and Ca-saturated and untreated samples, were modelled satisfactorily as R1-ordered P/S by the program NEWMOD-for-Windows. The unique composition of brinrobertsite relative to R1 IS, which is ubiquitous in metabentonites, was caused by leaching of alkalis and alkaline-earth elements by hydrothermal fluids associated perhaps with a nearby intrusion, as demonstrated by bulk-chemical analyses of the metabentonite. The crystal structure is modelled as having Al/Si distributions symmetrical by reflection across interlayers. This causes all 2:1 layers to be equivalent in having one tetrahedral sheet with little or no Al, and the other with significant Al substitution, giving rise to alternate high- and low-charge interlayers. Geological evidence suggests that brinrobertsite is a back-reacted product of hydrothermal alteration in the sequence: glass → pyrophyllite → brinrobertsite.

Apatite samples from rare-metal mineralization were investigated by a combination of cathodoluminescence (CL) microscopy and spectroscopy, microchemical analysis and trace element analysis. Internal structures revealed by CL can be related to variations in the crystal chemistry and may sometimes reflect changes in the composition of the mineralizing fluids.

Apatite from mineralization related to alkaline rocks and carbonatites (Type 1) typically exhibits relatively homogeneous blue and lilac/violet CL colours due to activation by trace quantities of rare earth element ions (Ce3+, Eu2+, Sm3+, Dy3+ and Nd3+). These results correlate with determined trace element abundances, which show strong light rare earth element (LREE) enrichment for this type of apatite. However, a simple quantitative correlation between emission intensities of REE3+/2+ and analysed element concentrations was not found.

Apatite from P-rich altered granites, greisens, pegmatites and veins from Sn-W deposits (Type 2) shows strong Mn2+-activated yellow-greenish CL, partially with distinct oscillatory zoning. Variations in the intensity of the Mn2+-activated CL emission can be related either to varying Mn/Fe ratios (quenching of Mn activated CL by Fe) or to self-quenching effects in zones with high Mn contents (>2.0 wt.%). The REE distribution patterns of apatite reflect the specific geological position of each sample and may serve as a “tracer” for the REE behaviour within the ore system. Although the REE contents are sometimes as high as several hundred parts per million, the spectral CL measurements do not exhibit typical REE emission lines because of dominance of the Mn emission. In these samples, REE-activated luminescence is only detectable by time-resolved laser-induced luminescence spectroscopy.

Both types of apatite (Type 1 in the core and Type 2 in the rim) were found in single crystals from the Be deposit Ermakovka (Transbaikalia). This finding proves the existence of two stages of mineralization within this deposit.

The first recorded occurrence of cummingtonite in the Scottish Dalradian is described. The mineral occurs in thin layers within a psammite-semipelite sequence forming the lower part of the Easdale Subgroup in which it coexists with bytownitic plagioclase, almandine-rich garnet and quartz. Textural and mineral chemical evidence suggest that the cummingtonite developed from hornblende during amphibolite-facies regional metamorphism. The protolith to this cummingtonite-bearing rock is believed to have been a basaltic tuff, possibly alkaline in character, containing a significant proportion of sedimentary detritus. The cummingtonite-bearing rock may provide the earliest record of basic volcanism in the Dalradian of the Ballater district.

The Island of Linosa is a small part of the large submarine volcanic complex which is locatedat the SW edge of the Linosa Graben, Sicily Channel. The island was formed between 1.06±0.10 and 0.53±0.07 Ma, through three main stages of activity: Paleo-Linosa, Arena Bianca and Monte Bandiera. Major and trace element data show that the compositional variability of the three activity stages is limited, with most of the rocks showing basaltic to hawaiitic composition. Evolved benmoreites and trachytes are foundas lithics in some pyroclastic units of Paleolinosa. The mafic rocks of the three stages show porphyritic texture, with phenocryst assemblages characterized by olivine, clinopyroxene and plagioclase. The volume ratio of olivine vs. clinopyroxene decreases from early to late stages of activity in mafic rocks with comparable major element composition. Clinopyroxene phenocrysts from mafic rocks of the three stages have poorly variable composition, clustering in the augite field. Phenocrysts from the first activity stage (Paleo-Linosa), show a slight increase in TiO2, Al2O3 and CaO, and a decrease of Fe2O3 (total) with the increasing SiO2 content of the host rocks. Crystals from the second and the third stage (Arena Bianca and Monte Bandiera) display a slightly more restricted range of FeOtot, frequently with very high MgO, Al2O3 and TiO2 contents. Crystal chemical investigation of clinopyroxenes from rocks of the three stages with comparable degrees of evolution, revealed significant variation of structural parameters, in particular VM1 and Vcell. These show a consistent decrease, passing from clinopyroxenes of the early stage to crystals extracted from the mafic lavas of stages 2 and 3. Given the similar compositional ranges of the host rocks, structural variations of clinopyroxenes are interpreted to reveal modifications of crystallization pressure, which increased, passing from Paleo-Linosa to the Arena Bianca and Monte Bandiera stages. Given this information, the observed crystal-chemical variations provide information on the depth of magma reservoirs and on the evolution of the plumbing system of Linosa volcano.

A combination of Kawai-type multianvil apparatus and highly brilliant X-rays at the third generation synchrotron radiation facility (SPring-8) in Japan has been successfully applied to various studies in high-pressure mineral sciences such as determinations of phase transition boundaries, P–V–T relations of high-pressure phases, kinetics of phase transitions, structure and viscosity of melts. These studies are now comfortably made at pressures of ˜25 GPa and at temperatures to 2300°C, using the intense X-ray beam and the large capacity of the high-pressure apparatus at SPring-8. Moreover, efforts have been made to further extend the pressure limit using large sintered diamond anvils. Thus in situ X-ray observations are now possible at pressures to 50 GPa with the Kawai-type apparatus, which may be doubled in the near future when the potential of sintered diamond anvils is fully utilized. On the other hand, some problems, such as those related to pressure and temperature measurement, have been manifested in these studies. These should be overcome for further quantitative studies of the mineralogy of the Earth's deep interior based on these techniques.

The studied gabbroic nodules occurring in the Petrazza pyroclastic rocks consist mainly of plagioclase (An95–87), olivine (Fo83-73) and clinopyroxene (Mg# 90–77), with subordinate opaques (Ti-magnetite) and amphibole (Mg-hastingsite), which constitute the cumulate minerals. Interstitial material has a relatively high, but variable, degree of vesicularity and consists of variable amounts of glass and quenched crystals of plagioclase (An71–55), amphibole, clinopyroxene and rare biotite, olivine and opaques. Silicate melt inclusions are abundant in the cumulate minerals, but complete homogenization to melt has been observed only in the inclusions occurring in clinopyroxene, where the temperatures of homogenization vary from 1134 to 1190°C. Microthermometric investigations of fluid inclusions and of the shrinkage bubble of the melt inclusions suggest that the magma contained CO2. The apparent scarcity of H2O indicates that this component was strongly partitioned into the magma at the time of crystallization of the investigated minerals; this is further supported by the occurrence of (1) daughter biotite- and amphibole-bearing inclusions which show that the H2O activity in the magma was sufficiently high to allow their crystallization, and (2) calcic plagioclase (An95–87) which can be crystallized from a high-alumina basaltic magma at pressure ≤2 kbar, temperatures in the range 1050–1100°C and in the presence of 3–4 wt.% of water (MELTS software simulations).

The composition of the melt inclusions suggests that the hosting plagioclase, olivine and clinopyroxene crystallized from slightly different batches of magma. The S content in the melt inclusions of clinopyroxene and olivine is high (up to 0.41 wt.%). The presence of Fe-Cu(-Ni)-rich blebs of sulphide in plagioclase, olivine, amphibole, and locally in the melt inclusions too, further supports the important role of sulphur in the primitive magmas of the investigated gabbros. Small differences in redox conditions or in the Fe content of the melts favoured S mobilization as sulphide.

Recent diamond-anvil cell experiments are providing windows of unprecedented clarity on the interiors of the Earth, other planets, and their moons from high P-T studies of the materials that comprise these bodies. With recent advances in techniques, the component minerals can be examined with a growing array of in situ methods over an expanding range of conditions that extend to hundreds of gigaspascals in pressure and thousands of degrees in temperature. Such investigations reveal that major, if not profound, changes in physical and chemical properties of these materials occur with depth. This information is crucial for understanding the materials basis of regional to global structure and processes documented by a wealth of recent observational and geophysical data. This paper reviews selected recent studies of major planet-forming minerals, focusing on key examples that illustrate different microscopic origins of macroscopic behaviour. This comparative mineralogical approach provides insight into phenomena occurring over a wide range of length scales. For terrestrial planets, the high-pressure behaviour of representative silicates, oxides and sulphides is examined. This includes the silicate perovskite assemblages that form the bulk of the Earth's lower mantle, for which a number of new findings concerning effects of non-stoichiometry and defect properties, pressure-induced electronic and magnetic transitions, and rheology have been obtained. High P-T studies of Fe-Ni alloys, together with various light elements, provide constraints on the composition, structure and dynamics of terrestrial planet cores. Water is a key component of many planetary bodies; as ice it undergoes numerous high-pressure transformations and as a volatile component it is involved in potentially important high P-T mineral reactions and is incorporated in dense mineral phases. Striking behaviour is observed in other molecular systems, including CO2 and CH4 and their mixtures with H2O; these form new phases, some relevant at the relatively modest conditions of deep marine sediments, others at the extreme states found in the deepest planetary interiors. Additional high P-T interactions between rare gases and ices and silicates are also documented. For the large planets, the most abundant ‘mineral’ is hydrogen, which has been shown to undergo novel mineral/gas reactions, possibly in cloud decks deep within the dense atmospheres of these bodies.

Verbeekite, ideally PdSe2, monoclinic with space-group choices C2/m, C2 or Cm; a = 6.659(7), b = 4.124(5), c = 4.438(6) Å, ß = 92.76(3)°, V = 121.7(4) Å3; a:b:c = 1.6147:1:1.0761, Z = 2, is a new, very rare, primary mineral, intimately associated with secondary oosterboschite {(Pd,Cu)7Se5}, from the Musonoi Cu-Co-Mn-U mine, near Kolwezi, Shaba Province, Democratic Republic of Congo. Additional associated minerals are Cu- and Pd-bearing trogtalite {(Co,Cu,Pd)Se2}, Se-bearing digenite and Se-bearing covellite. The strongest five lines of the X-ray powder-diffraction pattern {d in Å (I) (hkl)} are: 4.423(30)(001), 3.496 (30)(110), 2.718(100)(111), 1.955(50)(310 and 1.896(50)(12). The mineral has also been identified, as a single anhedral 25 µm-sized grain, from Hope's Nose, Torquay, Devon, England where it is associated with native gold, chrisstanleyite Ag2Pd3Se4, oosterboschite(?), unnamed Pd2HgSe3 and cerussite. At Musonoi, altered verbeekite grains do not exceed 200 µm in size and are anhedral, black, with a black streak and a metallic lustre. The mineral is opaque, brittle, has an uneven fracture, and lacks discernible cleavage. The VHN5 ranges 490–610, mean 550 kp/mm2 (2 indentations), roughly approximating a Mohs' hardness of 5Ý. Dcalc. = 7.211 g/cm3 for the ideal formula. Electron-microprobe analyses (mean of 4 spot analyses) yielded Pd 39.6, Cu 0.5, Se 58.8, total 98.9 wt.%. The empirical formula is (Pd0.99Cu0.02)σ1.01Se1.99, based on Pd+Cu+Se = 3. In plane-polarized reflected light, the mineral is a nondescript grey and is neither pleochroic nor perceptibly bireflectant. Anisotropy is moderate with rotation tints in varying shades of brown. Reflectance spectra and colour values are tabulated. The name honours Dr Théodore Verbeek (1927–1991) who was the first geoscientist to study the Musonoi palladium mineralization in the Democratic Republic of Congo (1955–1967) and who co-discovered this new mineral phase.

A new occurrence of barysilite, Pb8Mn(Si2O7)3, at the polymetallic Garpenberg Norra Zn-Pb deposit, Hedemora, Dalarna, Sweden, is described. The mineral, which forms colourless, transparent grains, is characterized by X-ray diffraction and electron-microprobe analyses. The assemblage includes tephroite, zincian jacobsite, manganoan diopside and others. The crystal structure of a barysilite crystal from Garpenberg Norra was redetermined using single-crystal X-ray diffraction data (Mo-Kα, CCD area detector) and has been refined in space group Rc with a = 9.804(1), c = 38.416(8)Å, V = 3197.8(8)Å3, to R1 = 2.32% for 1025 ‘observed’ reflections with Fo >4σ(Fo). A previous, low-precision structure determination (Lajzérowicz, 1965; R = 20%) is confirmed but improved considerably. The structure contains one distorted MnO6 polyhedron with six equivalent Mn–O bonds (2.224 Å), one Si2O7 disilicate unit with an Si–O–Si angle of 120.9°, and two non-equivalent Pb sites. The Pb1 site has a highly irregular, one-sided coordination with six O ligands, indicating a stereoactive 6s2 lone-electron pair on the Pb2+ ion, whereas the [6+3]-coordinated Pb2 site is fairly regular, with Pb–O distances of 2.540 (3×), 2.674 (3×) and 3.098 (3×) Å. The Pb2 site contains ~10% of Ca (+Ba) replacing Pb, corresponding to the structural formula Pb16(Pb,Ca)22Mn(Si2O7)3. This is the first direct proof that not only the M site in barysilite-type Pb8M(Si2O7)3 compounds can be replaced by divalent cations.