The 1800 m thick preserved remnant of the Tertiary lava succession of Mull and Morvern consists of three basic mantle-derived magma types, with compositions varying from tholeiitic to mildly alkalic, and from picritic basalts to trachytes. This results in a similarly wide range in mineral compositions. Contrary to the suggestions of previous workers the mineral chemistry of the lava succession (in conjunction with published major and trace element chemistry) is strongly supportive of a fractional crystallisation origin for the more evolved lavas.

Resorped and regrown (with more basic material) plagioclase phenocrysts found in the more-evolved are indicative of magma mixing processes involving replenishment of an evolving magma chamber with more-basic magma. Lavas containing 15–20 vol.% plagioclase phenocrysts probably represent eruptions from the top of a magma chamber where flotation cumulates of plagioclase had developed. Fragmental phenocrysts found in some highly plagioclase phyric lavas (from near the top of the preserved lava succession) suggest that the eruption of lavas may have been explosive.

A suite of ultramafic-mafic alkaline igneous rocks in the Damodar Valley, eastern India, contains carbonate, phosphate and titanate minerals that are not characteristic or common in minettes or lamproites, but are typical of orangeites (Group II kimberlite) from southern Africa. Phlogopite grains from the Damodar alkaline rocks yield mean 40Ar/39Ar ages of 116.6±0.8 Ma, 113.5±0.5 Ma and 109.1±0.7 Ma (1σ errors) using laser dating techniques. These ages are similar to the Rb-Sr ages of African orangeites, which lie mostly in the range 121 to 114 Ma. Prior to this study, only one possible occurrence of orangeite (the ∼820 m.y.-old Aries pipe, Western Australia) was known outside the Kaapvaal craton and its environs. If the Damodar alkaline rocks are bona fide orangeites, it is likely that they were generated at depths of >150 km, within the stability field of diamond.

Unusual corundum-bearing rocks occur in the Bond Range, northern Tasmania, in a hydrothermally altered Cambrian quartz porphyry. The assemblage exhibits quartz and corundum in mutual contact, a rare phenomenon, in association with andalusite, pyrophyllite, diaspore and other minerals. This metastable assemblage apparently resulted from advanced argillic alteration at moderate temperature and low pressure, followed by rapid depressurisation accompanying boiling of hydrothermal, granite-derived fluids. This corundum occurrence appears to be unrelated to the sapphires in placer deposits in Tasmania.

The occurrence of MnO exsolution in periclase host crystals from Långban, Sweden, is described. The composition of the periclase is Mg0.942 Mn0.046Zn0.012O, and it coexists with exsolved manganosite crystals with a composition of Mn0.909Mg0.082Zn0.008O. Crystals of hausmannite are also present, indicating fO2 conditions approaching the MnO–Mn3O4 equilibrium.

Activity-composition data for the system MgO–MnO is critically reviewed. The data obtained from solid electrolyte measurements are rejected because of the unrealistic calculated equilibration temperatures and the large deviations from the gas equilibration Mn-Pt activity measurements. The large errors associated with the gas equilibration measurements, especially at large XMnO, also introduces uncertainties associated with the asymmetric interaction parameters. The non-parametric ‘jack-knife’ method was used to determine the asymmetric interaction parameters and their standard deviations from the data of Wood et al. (1994) and Tsai and Muan (1992). These were calculated as WMnO = 21.2 kJ/mol, σWMnO = 2.5 kJ/mol and WMgO = 8.2 kJ/mol, σWMgO = 3.3 kJ/mol.

Using the asymmetric interaction parameters, WMnO = 19.9 kJ/mol and WMgO = 13.7 kJ/mol for the system MgO–MnO as determined by Wood et al. (1994) and the equations for two-phase equilibrium as formulated by Thompson (1967), equilibration temperatures of 334°C and 466°C were calculated. The difference between the calculated temperatures is ascribed to inaccuracies in the experimentally determined interaction parameters.

Th-rich (up to 18.4 wt% ThO2) loparite occurs as an accessory phase in foyaite pegmatites at Mt. Eveslogchorr, Khibina complex, Russia. It is associated with aegirine, astrophyllite, eudialyte, lorenzenite, lamprophyllite, magnesio-arfvedsonite and gerasimovskite. Loparite crystals are zoned from niobian loparite (core) to niobian thorian and thorian niobian loparite (rim). Th-enrichment is accompanied by a decrease in Na, LREE, Sr and increase in A-site vacancies. The most Th-rich composition approaches (Na0.39LREE0.19Th0.12Ca0.05Sr0.02)Σ0.77(Ti0.76Nb0.27)Σ1.03O3. The mineral is partly or completely metamict and after annealing gives an X-ray diffraction powder pattern similar to that of synthetic NaLaTi2O6 and naturally occurring loparite of different composition. For the Th-rich rim sample, the five strongest diffraction lines (Å) are: 2.72 (100) 110, 1.575 (60) 211, 1.925 (40), 1.368 (30) 220, 1.222 (20) 310; a = 3.867(2) Å. The X-ray diffraction patterns do not exhibit peak splitting or other diffraction lines typical of low-symmetry and ordered perovskite-type structures. Composition determinations, infrared transmission spectroscopy and X-ray diffractometry show that thorian loparite is partly replaced by betafite with LREE and Th as dominant A-site cations (‘ceriobetafite’). Some loparite samples also exhibit thin replacement mantles of belyankinite with high LREE2O3 and ThO2 contents. Both ‘ceriobetafite’ and belyankinite were formed due to metasomatic alteration of loparite.

Zircon frequently occurs as a minor mineral in kimberlites, and is recognised as a member of a suite of mantle-derived megacryst minerals. Cathodoluminescence (CL) microscopy and laser ablation ICPMS analysis were used to study the internal structure and chemical composition of zircon crystals from southern African kimberlites. Zoning revealed by CL ranges from fine oscillatory to broad homogeneous cores and overgrowths. The ICPMS data show that kimberlite zircons have distinctive trace element contents, with well defined ranges for REE, Y, U, Th, P and some other trace elements. Both low REE contents (ΣREE < 50 ppm), and distinctive chondrite-normalised REE patterns with low and flat HREE are characteristic of kimberlite zircons. Samples or zones with yellow CL have higher Th, U, Y, and REE than those with blue-violet CL. Variations in the concentrations of a range of trace elements lead to different amounts of lattice defects, creating the possibility for different levels of direct excitation of luminescence centres, and therefore different CL colours. The distinctive CL and compositional features described here can rapidly identify kimberlite zircons in prospecting samples taken during exploration for kimberlite bodies.

The rare mineral otavite CdCO3 was found at the abandoned Pb-Zn mine of Montevecchio (SW Sardinia, Italy). Otavite occurs in the oxidised gossan, in association with aurichalcite. SEM imaging shows that otavite is composed of lenticular hollow structures containing aggregates of tiny rhombohedral crystals. Oxidation of primary Cd-bearing sulphides (sphalerite and greenockite) releases up to 24 ppm of Cd to drainage waters of the Montevecchio area. These waters are generally saturated with respect to otavite. Therefore, this mineral might play an important role in controlling Cd mobility in the environment.

Tamarugite (NaAl(SO4)2.6H2O) occurs at Compton Chine (NGR SZ 36808513), on the Isle of Wight, U.K., as globular encrustations covering an area of 2.8 m2 on argillaceous pyritous siltstones of the Lower Greensand Group, Lower Cretaceous. It is proposed that the production of H2SO4 from oxidizing pyrite in the siltstones releases Al ions from the argillaceous sediments, the Na content being acquired from sea spray. An analogy is made between Compton Chine and an occurrence in Victoria, Australia.

Melt generation during granulite-grade metamorphism is believed to be controlled by the stability temperatures of biotite, whose breakdown provides H2O and controls fluid-absent melting in the lower crust. In a simple KMASH system, the restite minerals crystallising due to incongruent melting of phlogopite depend upon the bulk composition. In an alumina-poor and silica-rich portion of the system (Phl + Qtz), enstatite appears with the melt, while in an alumina-rich system (Phl + Sil + Qtz) cordierite appears first instead of enstatite. Since the temperature of biotite stability is believed to be strongly controlled by its F and Ti content, it will have significant effect on the fluid-absent melting reactions during granulite-grade metamorphism of mica-containing granites as well as pelitic rocks in the deeper crust.

To understand such effects in an aluminous portion of the KMASH system, experiments were performed (between 850 and 1100°C and at 7, 10 and 12 kbar) with bulk composition containing 2Phl-6Sil- 9Qtz, where natural phlogopite with F/(F+OH) = 0.39 and Mg/(Mg+Fe) = 0.96 was used. In runs with this charge and containing 5 wt.% of excess water, cordierite appeared around 920°C at 7 kbar and 990°C at 12 kbar, and it disappeared at about 1080°C with the appearance of 221 sapphirine. In fluid-absent runs, these boundaries marginally shift to higher temperatures (30-50°C). The enstatite which was distinctly absent in H2O-saturated runs, crystallises in the high-temperature sapphirine field with up to 12 wt.% Al2O3 in H2O-undersaturated runs. The enstatite formation with cordierite is perhaps inhibited due to the Al consumption by cordierite and instability of Al-free enstatite at temperatures of cordierite stability. Re-equilibrated phlogopite persists in both the cordierite and sapphirine fields. The temperatures of the beginning of phlogopite breakdown are about 100-140°C above those reported for reaction Phl + Qtz → En + Sa + L (Vielzeuf and Clemens, 1992) with F and Ti-free phlogopite, but are ≈50–100°C lower than the temperatures reported (Tareen et al., 1995; Dooley and Patino Douce, 1996) for the same reaction containing F- and Ti- bearing phlogopite. The combined effect of the F and Ti content in phlogopite on its stability temperatures in the KMASH system has been found to be additive in relation to those containing only F or Ti. H2O-saturated runs produced per-aluminous melts with ≈27 wt.% Al2O3 in the cordierite field and ≈23% Al2O3 in the sapphirine field. The H2O-undersaturated runs produced melts rich in K2O (≈10 wt.%), SiO2 (72.5 wt.%) and relatively poor Al2O3 (12 wt.%).

Widespread secondary andradite-grossular-hydrogrossular garnet, epidote, prehnite and titanite occur throughout the Galway Granite and its satellite plutons (Roundstone; Inish; Omey and Letterfrack) and even in some of the country rocks several kilometres from the granites. These minerals are not found in low CaO (<1%) granites. They formed as result of secondary fluid movements which altered the biotite, plagioclase and hornblende and also produced sericite and chlorite.

Mereheadite, ideally Pb2O(OH)Cl, is a new mineral related to litharge and which is structurally similar to synthetic bismuth-oxyhalides. With other lead- and lead-copper oxychlorides, it occupies lenses and cavities in veins of manganese and iron oxide minerals which cut through a sequence of dolomitic limestones at Merehead quarry, Cranmore, Somerset (51°12′N, 2°26′W) Mereheadite is pale yellow to reddish-orange, transparent to translucent and has a white streak and a vitreous or resinous lustre. It is not fluorescent. Individual grains, up to a few mm across, cluster together in compact masses of 10–30 mm in size, but discrete crystals have not been observed. Specular reflectance data on randomly orientated grains from 400 to 700 nm are provided, and refractive indices calculated from these at 590 nm range from 2.19 to 2.28. H = 3.5, VHN100 = 171, D(meas) = 7.12(10) g/cm3, Dcalc = 7.31 g/cm3. The mineral is brittle with an uneven, conchoidal to hackly fracture and has a perfect (001) cleavage which is parallel to the sheets of PbO and Cl. It is intimately associated with mendipite, blixite, cerussite, hydrocerussite and calcite in lenses and pods in the veins. Other minerals which occupy cavities in these veins include chloroxiphite, paralaurionite, parkinsonite and the borosilicate datolite. Mereheadite is monoclinic, space group C2/c, and its cell parameters, refined from powder X-ray diffraction are: a = 5.680(2), b = 5.565(3), c = 13.143(9) Å, β=90.64(4)°, V = 415.4 (8) Å3, Z = 4. The ten strongest reflections in the X-ray powder diffraction pattern are [d in Å, (I, hkl)]: 2.930(10,113), 3.785(5,111, –111), 2.825(4,200), 6.581(4,002), 2.182(4,115), 2.780(4,020), 3.267(4,004), 1.980(3,–220), 1.695(3,224,132,117), 1.716(3,026). Its empirical formula is Pb8O4.19(BO3)0.51 (CO3)0.62(OH)0.76Cl4.09. Although it is very similar chemically to blixite, it has notably different cell parameters. There is some uncertainty about the essential nature of boron and carbon in natural mereheadite. This stems from the impossibility of ensuring the purity of samples for wet-chemical analysis, and from the predominance of lead in the structure of the mineral which has meant that the location of boron and carbon within the mereheadite structure is unresolved, 11B MAS NMR does show, however, that boron is present as BO3 groups. The structure consists of alternating PbO sheets and layers of chlorine atoms. Each lead atom is coordinated to four chlorines and four O/OH in a square antiprism configuration. As such, it is structurally-related to nadorite, thorikosite and schwartzembergite. Comparisons with structurally analogous phases such as bismuth oxychlorides and bismutite (Bi2O2CO3) suggest that the BO3 and CO3 groups are likely to replace chlorine in the layer between PbO sheets. The composition of natural mereheadite is defined by three end-members: the mereheadite end-member Pb2O(OH)Cl, and two fictive end-members Pb2(OH)2CO3 and Pb4O(OH)3BO3.

The Långban, Nordmark and Jakobsberg Mn-Fe deposits contain the only known occurrences of filipstadite and manganostibite (ideal formulae (Mn, Mg)2(Sb0.55+Fe0.53+)O4 and Mn72+SbAsO12, respectively). Filipstadite from Nordmark is newly recognized, and occurs in assemblages with svabite-johnbaumite, calcite, tephroite-forsterite, phlogopite-kinoshitalite, tilasite, ±jacobsite, ±plumbia roméite, ±adelite, ±hedyphane. Manganostibite from Långban and Jakobsberg is reported for the first time, and the mineral is generally associated with katoptrite, tephroite, humite-group minerals, calcite, svabite, allactite, manganosite, hausmannite, jacobsite, spinel s.s., etc. Whereas filipstadite is clearly secondary relative to the major part of the matrix components, manganostibite is believed to have formed coevally with the principal ore and skarn minerals at these deposits.

The previously known compositional ranges are extended. Based on electron-microprobe analyses, Nordmark filipstadite contains 4.1–7.3 MgO, 0.0–0.5 Al2O3, 30.5–45.3 MnO, 17.0–40.1 Fe2O3, 0.2–0.9 ZnO, 19.9–29.9 Sb2O5 (all in wt.%), corresponding to 58–100 mol.% of a pure filipstadite component. Associated jacobsites show Sb2O5 contents of up to c. 5 wt.%. Manganostibites (all three deposits considered) contain 1.0–2.9 MgO, 2.8–3.8 SiO2, 57.4–60.3 MnO, 0.2–3.5 Mn2O3, 0.3–2.0 Fe2O3, 0.0–2.4 ZnO, 21.5–23.0 Sb2O5, 7.7–10.0 As2O5 (all in wt.%). Si and trivalent cations are incorporated via a (Mn3+,Fe3+) + Si4+=Mn2+ + As5+ exchange mechanism, which improves the local charge balance at tetrahedral structural sites dominated by As.

The micro-inclusions located in the genetic centre of Yakutian diamond monocrystals have been studied using optical (anomalous birefringence, photoluminescence, cathodoluminescence) and microanalytical (electron-microprobe, proton-microprobe, scanning electron microscope) methods. Most diamonds nucleated heterogeneously on mineral seeds, that lowered the energy barrier to nucleation. Nucleation of peridotitic diamonds occurred on a matrix of graphite+iron+wüstite, in an environment dominated by forsteritic olivine and Fe-Ni sulfide. Nucleation of eclogitic diamonds occurred on a matrix of sulfide ± iron in an environment dominated by Fe-sulfide and omphacite (±-K-Na-Al-Si-melt). The mineral assemblages recorded in the central inclusions of Yakutian diamonds indicate that they grew in a reduced environment, with oxygen fugacity controlled by the iron-wüstite equilibrium. Nucleation of diamond occurred in the presence of a fluid, possibly a volatile-rich silicate melt, highly enriched in LIL (K, Ba, Rb, Sr) and HFSE (Nb, Ti, Zr) elements. This fluid also carried immiscible Fe-Ni-sulfide melts, and possibly a carbonatitic component; the introduction of this fluid into a reduced refractory environment may have been accompanied by a thermal pulse, and may have created the conditions necessary for the nucleation and growth of diamond.

W-bearing rutile formed during alteration of jarosite by resurgent hydrothermal fluids in the oxide zone of the Kori Kollo gold deposit. The rutile shows sector zoning in basal sections and well developed multiple growth zones, both defined in backscatter electron images by variations in the W content. The maximum WO3 content is 5.3 wt.% and W substitutes for Ti with double substitution of Fe to maintain charge balance. The causes of multiple growth bands are considered to be changes in externally controlled variables occurring in a shallow hydrothermal system. Whereas Ti is probably leached from biotite in dacitic rocks, the W is introduced by hydrothermal fluids.