The Older Giant Dyke Complex is a differentiated alkaline intrusion of Proterozoic age (1154±16 Ma) and is the earliest of the late Gardar intrusions in the Tugtutôq-Ilímaussaq region. The dyke is approximately 20 km long by 0·5 km broad and comprises (i) marginal ‘border group’ rocks of alkali olivine gabbro, grading inwards to ferro-syenogabbro and (ii) an axial ‘central group’ of salic rocks ranging from augite syenite in the WSW to sodalite foyaite in the ENE.

Chilled margins contain plagioclase (An53), olivine (Fo53), magnetite, ilmenite, and apatite as liquidus phases and later-crystallized augite (Di69Hd27Ac4) and biotite (Annite32). The coexisting Fe-Ti oxides indicate fO2 and T values just below the synthetic QFM buffer curve. In the border group, plagioclase cores zone into anorthoclase and soda-sanidine rims, olivines reach Fo16, pyroxenes Di32Hd59Ac9, and biotites Annite86. Interstitial pargasitic amphibole appears close to the innermost margins. In the central group, feldspars are all perthitic alkali feldspars and nepheline becomes a major, early crystallizing phase. Olivines range from Fo10-Fo4, in the augite-syenites where they coexist with ferro-salites Di50Hd47Ac3, but olivine is absent from foyaitic assemblages in which the pyroxenes range through aegirine-augite to pure aegirine. Interstitial amphiboles range from ferro-pargasite or hastingsite to katophorite and thence towards arfvedsonite, but are absent from the most differentiated rocks, whereas biotite occurs throughout the entire group in the range Annite71-Annite100.

The parental magma, represented by the chilled margins, was a relatively anhydrous alkali olivine-basalt with an initial 87Sr/86Sr ratio of 0.70326. Its high Ti, P, Ba, and F contents are inferred to be features inherited from a primary magma, derived from the mantle as a small partial melt fraction which involved significant amounts of fluor-apatite and phlogopite. While all lithologies are considered as differentiates from this parental magma, there is both a well-defined field junction and a compositional hiatus between the border group and the central group rocks. Mineralogical considerations and REE patterns suggest that the later, more salic (?benmoreitic) magma from which the central group crystallized, related to the parental magma by ol-fsp-ap-FeTi oxide fractionation. Congelation in both border group and central group occurred by side-wall crystallization, but the salic magma became compositionally stratified, with upward concentration of alkalis and volatiles to produce a phonolitic upper facies which is preserved at the ENE end of the intrusion owing to subsequent axial tilting.

Data for U, Th, and K, determined by epithermal neutron activation methods, are reported for Lower and Middle Dalradian lithologies from Co. Donegal, Ireland. Abundances are identical to rocks with stratigraphical correlation in the Scottish Dalradian and appear not to have been affected by regional metamorphism to biotite and possibly even garnet grade during the Grampian orogenic phase, or later contact metamorphism in the aureole of the Main Donegal pluton. Uraniferous Dalradian lithologies have not been encountered in Donegal. Incorporation of Dalradian rocks, either by assimilation or as extensive raft trains within the Main Donegal granite, is therefore unlikely to have contributed to the development of known pegmatite-hosted U mineralization associated with this late Caledonian pluton.

Högbomite occurs in two contrasting mineral assemblages within the Currywongaun-Dough-ruagh intrusion of north Connemara: a cordierite-rich pelitic xenolith and an orthopyroxenite. In the latter, högbomite and green spinel form blebs within magnetite-ilmenite grains. The högbomite displays significant compositional variation from grain to grain: TiO2 (3.0–6.3%), FeO (21.6–21.3%), MgO (10.0–7.5%), ZnO (3.6–2.4%). This chemical heterogeneity appears to represent variable degrees of partial substitution of Mg and Zn by Ti, in the replacement of spinel by högbomite. By contrast, in the cordierite-hornfels, the högbomite compositions are more notably enriched in iron: TiO2 (4.7–7.0%), FeO (29.6–24.3%), MgO (4.2–6.2%), ZnO (2.7–2.1%). This iron-rich högbomite appears to have formed primarily by interaction between opaque ore and adjacent cordierite, rather than by replacement of spinel.

Two high-grade metamorphic episodes appear to be necessary for högbomite growth, one determining chemical composition and the other appropriate physical parameters. In the Connemara occurrences thermal metamorphism and partial melting, coupled with contamination of the surrounding magma, controlled the formation of mineral assemblages rich in Fe, Mg, Al, Ti, and Zn. Emplacement of the intrusion was accompanied by amphibolite facies regional metamorphism and it is to this metamorphic event that the growth of högbomite may be attributed.

Partially melted basalts enclosing amygdales which have been completely melted formed at Scawt Hill adjacent to a Tertiary dolerite plug. Melting of the basalts commenced in a clay-rich mesostasis to produce a feldspathic liquid which then crystallized to an assemblage of dendritic olivine, skeletal hypersthene, opaque oxide and Mg-hercynite in a microcrystalline plagioclase matrix. An original mineral assemblage of zeolite, calcite, and saponite-nontronite in the amygdales melted and quenched to a brown glass now containing complexly zoned pyroxenes with plagioclase and opaque oxide. Melting commenced between 700–800°C, reaching a maximum temperature of 1168°C, and was followed by rapid cooling. The assimilation of remelted basalt may alter the course of crystallization of contaminated magmas.

Bredigite is a constituent of the very high-temperature, low-pressure, exomorphic suite of Carneal, Co. Antrim. Although this mineral is very rare in nature, it is an important constituent of some slags and cement clinkers but there has been much controversy about its nature, most of the evidence having come from artificial materials. Chemical analysis of the Carneal mineral shows it to be remarkably similar to that from the type locality, Scawt Hill (also analysed here), and that it is an individual mineral species of generalized ionic composition (Ca,Na)14(Mg,Fe2+Fe3+Mn)2(Si,P)8O32. Ba (abundant in the original analysis of the slag mineral) is not a constituent. Accurate X-ray powder data of the natural mineral are given. Bredigite is not Ca2SiO4, nor is it part of a solid solution of variable composition between larnite and merwinite. Analyses are presented for the associated minerals larnite (allowing appraisal of its composition), spurrite, and spinels. The paragenesis is discussed.

The Tyndrum Pb-Zn mineralization occurs as veins and vein breccias in NE-SW trending fractures associated with the Tyndrum-Glen-Fyne fault. The major minerals are quartz, galena, and sphalerite with minor chalcopyrite and baryte. Tetrahedrite (sometimes silver-and cadmium-rich), pyrargyrite, marcasite, and pyrite occur as small inclusions (< 100 µm) in the galena-rich veins. Sphalerite formed early in the depositional sequence, mainly in breccias, with increasing amounts of galena and chalcopyrite deposited in the later vein stages of mineralization. Uraniferous veins post-date the main Pb-Zn mineralization and contain uraninite, calcite, baryte, galena, sphalerite, chalcopyrite, argentite, chalcocite, tetrahedrite, and safflorite.

Fluid inclusion studies reveal that the mineralizing solutions contained c.20 wt. % equivalent NaCl + KCl, had an Na/K ratio of 3 : 1 and were boiling during mineral precipitation.

The Tyndrum fault controlled the upward flow of the hydrothermal solutions and its intersection with fractures in quartzites favoured the siting of the veins. The depositional sequence is explained by an increase in temperature during the mineralizing episode. The uraniferous veins may be a late oxidized stage of the main Pb-Zn mineralization.

The dissolution rates of spheres of two magnesian olivines, two plagioclases, and quartz in tholeiitic basalt have been determined at three super-liquidus temperatures and one-atmosphere pressure. There are considerable differences in the rates among the minerals, e.g. at 1210°, 12° above the liquidus temperature of the basalt, labradorite dissolves at 86 µm/h. and the magnesian olivines at 9 and 14 µm/h. The rates are not time dependent and this, coupled with the existence of concentration gradients in the composition of quenched melt adjacent to partially dissolved crystals, indicates that the dissolution rates are dictated by a combination of diffusion and convection of components to and from the crystal-liquid interface. Values for the activation enthalpy of dissolution are small for quartz and plagioclase (40–50 kcal mol−1) but large for olivine 73–118 kcal mol−1). Dissolution of plagioclase in rock melts seems to be a much more rapid process than crystal growth, whereas olivines apparently dissolve and grow at similar rates. Crystal dissolution is sufficiently slow that ascending, crystal-bearing magma may become superheated and yet fail to dissolve the crystal fraction before quenching; this may be the reason that olivine phenocrysts are often rounded.

The peraluminous granitoid intrusions of southern Nova Scotia contain several mineralogical expressions of the excess alumina, including variable amounts of cordierite, in different textural types of granitoids, ranging from fine-grained aplites through coarser grained monzogranites and granodiorites, to very coarse-grained pegmatites. A detailed study of the spatial, textural and chemical characteristics of these cordierites suggests that the majority are of relict metamorphic origin, but that primary magmatic cordierites, as well as cordierites which grew in equilibrium with a water-rich fluid phase, also occur.

Potassium pargasite containing 3.19 wt. % K2O was found in a skarn from the islet of Einstödingen, Lützow-Holm Bay, East Antarctica, together with some high potassium pargasitic amphiboles. A positive correlation is shown between Fe2+/(Mg+Fe2+) and K/(K + Na(A)) ratios in pargasitic amphiboles suggesting that the increase of Fe2+ serve to stabilize high-K pargasites under the metamorphic conditions of the granulite facies.

The absorption spectrum of Ti3+ in quartz is typical for that element in an octahedral site, except for the high oscillator strength of the band which indicates intensive charge transfer, most likely between a substitutional Ti4+ and an interstitial Ti3+. The biaxial anisotropy of the band is similar to that of octahedral Fe2+ in the same crystal, suggesting the same site for the Ti3+, an interstitial site at the intersection of the threefold axis with two twofold axes. The dynamic nature of the Ti and Fe ions is indicated when the crystal is subjected to X-irradiation and then to bleaching treatment with UV-light or heat. Ti(IV) ions are acceptors of electrons donated by Fe2+ during X-irradiation. This is indicated by increase of the 2.4 eV band intensity with decrease in the Fe2+ band intensities and appearance of Fe3+ charge transfer bands in the UV-region. Heat and UV-light treatment decrease the Fe3+ CT bands and increase the Fe2+ crystal-field bands along with decrease in the 2.4 eV band related to titanium.

Hydroxyl-bastnaesite-(Nd), the Nd- and OH-dominant new member of the bastnaesite group, has been found in the red karstic bauxites near Nikšić, Montenegro. It occurs as whitish, irregular aggregates of crystals usually 100–200 µm in diameter. Hexagonal with the cell dimensions a = 7.191 and c = 9.921 Å, with Z = 6. The strongest lines of the X-ray powder diffraction pattern (d, I, hkl) are: 4.95 80(002); 3.596 79(110); 2.911 100(112); 2.077 29(300); 2.042 51(114); 1.914 30(302). The mineral is uniaxial positive, ω 1.715, ɛ 1.81; Dcalc 4.89 g/cm3.

Electron probe analysis, using garnet, apatite and synthetic glass standards, combined with thermogravimetric and evolved gas analysis, gave Y2O3 0.2, La2O3 27.1, Ce2O3 0.3, Pr2O3 8.5, Nd2O3 31.5, Sm2O3 4.4, Eu2O3 1.3, Gd2O3 1.4, CaO 0.3, F 3.3, H2O 2.26, CO2 20.63, sum 101.19, less O = F 1.39, total 99.80%. This analysis calculates to (Nd0.41La0.36Pr0.11Sm0.06Gd0.02 Eu0.02Ca0.01)Σ0.99(CO3)1.03[(OH)0.55F0.38]Σ0.93, or ideally, (Nd,La)CO3(OH,F), with Nd > La and OH > F.

The lead silicate minerals from Franklin, New Jersey, occurred in two separate assemblages. One of these is characterized by esperite associated with hardystonite and occasional larsenite. The second assemblage can be considered as two parts: one consists of margarosanite, barysilite, nasonite, and ganomalite; the other contains roeblingite and hancockite, together with a number of highly hydrated phases. Chemical analyses indicate that these species conform to their theoretical compositions. There are no simple lead silicates at Franklin; all are compound silicates of Pb with Mn, Zn, and Ca.

Uranoan thorite crystals have been found occurring as a sparse constituent in lithophysae in 6.1 to 6.8 Ma alkali rhyolite flows at Thomas Mountain, Utah, USA. The crystals are associated with sandidine, quartz, topaz, hematite, magnetite, and calcite; they are leek to dark grass green, transparent, well-formed, euhedral prisms, showing development of forms {100}, {101}, and {111}. The mineral is both optically isotropic, with a refractive index of 1.86(1), and X-ray amorphous, indicating its metamict state. Electron microprobe analysis yields: SiO2 17.3, ThO2 56.8, UO2 25.4, total 99.5%, and a structural formula of (Th0.72U0.31)Σ1.03Si0.97O4.

This appears to be the first reported occurrence of thorite in volcanic rocks of rhyolitic composition, and may account for part or all of the Th reported in alkali rhyolites and so-called ‘topaz-rhyolites’ of the western USA.

In southern Kerala, India, chrysoberyl occurs in granitic pegmatites in association with quartz in alkali feldspar and is thought to crystallize earlier than beryl and sillimanite. The pegmatites are thought to have derived from the residual melts of granitic liquids formed by partial melting of the khondalites. In the absence of pyrometasomatic, desilication or aluminium-contamination processes, the genesis of chrysoberyl is explained by the CO2 activity in residual melts. This model is at variance with the known concepts and may also explain the genesis of chrysoberyl in Sri Lanka where it is still controversial.

Qandilite, a new species of the spinel group, has been found in a forsterite-rich rock in contact with a kaersutite-rich banded diorite from the Qala-Dizeh region, NE Iraq. Chemical analysis yielded MgO 29.62, FeO 10.32, MnO 0.76, Fe2O3 28.27, Al2O3 4.83, TiO2 26.41, SiO2 0.02, sum 100.23 wt. %. This analysis calculates to [(Mg1.20Ti0.60)][Mg0.12Mn0.02)(Al0.17)]O4 with a composition of Mg2TiO4 63.8, MgFe2O4 12.8, FeFe2O4 23.4 mole %. Qandilite is cubic with a = 8.4033±0014 Å; cell volume 593.40 Å3 and space group Fd3m; Z = 8. The seven strongest lines in the X-ray diffraction pattern are (d,I,hkl): 2.971, 30, (220); 2.53, 100, (311); 2.101, 45, (400); 1.617, 50, (333, 511); 1.486, 60, (440); 1.0938, 30, (553, 731); 0.9704, 25, (555, 751). The colour is black, lustre metallic, streak black, fracture even and the cleavage perfect on (111). It is opaque, strongly magnetic, Dcalc = 4.04, Dmeas = 4.03, and VHN100 = 960–1045 kg/mm2, with H-7. The reflection colour is grey with a pinkish tint; it is isotopic with no internal reflections. Reflectance measurement data in air and oil in the range (400–700 nm) are given. Colour values for illuminant C in air and oil in terms of CIE colour space are: x = 0.307, 0.307; y = 0.311, 0.310; Y% = 13.10, 3.0; λd = 465, 460; and Pe% = 2.0, 2.2. Calculated data for the absorption coefficients (k) and refractive indices (n) in the range 400–700 nm are also presented.