The albitisation of pelitic metasediments to form adinoles adjacent to minor mafic intrusions has in the past been attributed to Na-bearing metasomatizing fluids emanating from the intrusions themselves. The chemistry and mineralogy of adinoles associated with dykes forming a high-intensity swarm in the Tallaght area, County Dublin, Ireland, confirms a metasomatic origin for the adinoles described, with Na and to a lesser extent Ca introduced into the country rocks at the expense of K. We suggest, however, that the source of the metasomatizing fluids was external to the dykes — possibly involving a hydrothermal system driven by an underlying magma reservoir that was parental to the dykes and also contributed volatiles to the hydrothermal system by degassing. Heat flow from the dykes was instrumental in promoting the reaction between muscovite in the country rock pelites and the Na(Ca)-bearing fluids to form albite, temperatures of ∼350°C in the country rocks within a metre of the contact being indicated. The mechanism of adinolization proposed is shown to be compatible with recent experimental work on the hydrothermal alteration of greywackes and basalts and also with the likely temperature gradients adjacent to dykes.

Albitite, locally aegirine- and riebeckite-bearing, formed as a result of sodium metasomatism of felsic dykes and argillites along the Melones Fault Zone near Jamestown, California. Pyrite, magnetite, hematite and titanite are common in small amounts in altered dykes. The dykes were originally plagioclase-hornblende porphyritic, and had major and trace element abundances typical of calc-alkaline rocks, whereas they now have Na2O contents as high as 11.40%. Associated fracture-filling veins are dominated by albite, but locally include aegirine, analcime, paragonite, calcite and sodic scapolite. Quartz is present in most albitic rocks, but is absent in riebeckite- and aegirine-bearing samples. Albitization predated CO2 metasomatism and formation of sericite-pyrite assemblages that are typical of gold deposits of the Mother Lode Belt.

Alkaline fluids responsible for Na-metasomatism had elevated Na+/K+ and Na+/H+ relatively high fO2, and low aH4SiO4. The presence of titanite indicates fluid. The presence of titanite indicates fluid XCO2 was low, in contrast to fluids that formed later carbonate-bearing assemblages. Sodic scapolite suggests that, at least locally, the fluids attained very high salinities.

Mass balance calculations indicate that alteration involved addition of large amounts of sodium, and the removal of SiO2 and K2O. Textural preservation, combined with volume factors calculated from specific gravity and whole rock analytical data, indicate that Na-metasomatism was essentially isovolumetric.

Sodium-rich zones along the Melones Fault Zone are closely associated with fault-bounded bodies of ultramafic rock, typically altered to talc-carbonate or quartz-magnesite-Cr muscovite assemblages. Carbonatization and talc-forming reactions in the ultramafic rocks may lead to SiO2-undersaturated fluids. Expansion of the muscovite stability field in terms of Na+/K+-Na+/H+, as a result of incorporation of Cr (up to 7.7% Cr2O3) in muscovite, would result in H+- and K+-depletion as the fluid interacts with ultramafic rocks. This could lead to fluids with elevated Na+/K+ and high pH, as documented in this occurrence.

The rare Li-mica taeniolite is described from the Dicker Willem carbonatite complex, Namibia, and from the Alpine carbonatitic lamprophyre dyke swarm at Haast River, New Zealand. At Haast River, taeniolite occurs in sodic and ultrasodic fenites derived from quartzo-feldspathic schists and rarely in metabasites, adjacent to dykes of tinguaite, trachyte and a spectrum of carbonatites ranging from Ca- to Fe- rich types. In Namibia, taeniolite is present in potassic fenites derived from quartz-feldspathic gneisses and granitoids at the margin of an early sövite phase of the complex and in a radial sövite dyke emanating from this centre.

The occurrence of taeniolite in these totally disparate carbonatite complexes, together with examples of lithian mica from other carbonatite complexes worldwide, raises the question of the status of Li as a ‘carbonatitic element’. We argue that lithium is not a consequence of crustal assimilation or interaction, but reflects the geochemical character of the magmatic source. Li, an overlooked and little-analysed element, may be an integral part of metasomatic enrichment in the mantle, and of magmas derived by partial melting of such a source.

Mineralogical, geochemical and isotopic data including K-Ar age determinations are presented for one of the largely unknown, Mesozoic ultramafic (lamproitic) occurrences of the Aldan Shield. Ultramafic, ultrapotassic rocks occur as isolated pipes or as dykes in alkaline complexes as the Yakokut complex. K-Ar dating of phlogopites from different ultramafic dyke rocks of Yakokut give cooling ages of 133.3 ± 1.3 Ma. These rocks generally contain olivine, clinopyroxene, phlogopite and spinel phenocrysts. Olivines are forsterite-rich (Fo86–94) and undeformed, suggesting that they are phenocrysts. The low Ti and Al contents of clinopyroxenes are close to those of lamproites. Phlogopite cores are rich in Al2O3 and TiO2 relative to the rims with two different zonation trends caused by distinct crystallization conditions after emplacement. Spinels are Ti-bearing magnetites and Ti-Al-magnesiochromites with high Cr/(Cr+Al) ratios (> 0.9), indicating their crystallization from a lamproitic melt.

Geochemically, the rocks are ultrabasic — basic with high mg# values, low Ca, Al, Na and strong enrichments of Rb, Ba and K. Their CaO/Al2O3, Zr/Nb or Ba/Sr ratios indicate their lamproitic nature and origin in the subcontinental lithosphere of a depleted mantle source which had undergone metasomatic enrichment. As the rocks all show strong negative Nb anomalies and low Ti, Y and Yb contents, the enrichment is attributed to subduction zone fluids. The Sr-Nd-data (87Sr/86Sr0 0.70573−0.70605 ± 0.00003; ɛNd − 10.2 ± 0.7) indicate the origin by partial melting of a heterogeneous mantle source with relatively low Rb/Sr ratios and an early enrichment. The evolution model comprises a depletion of ‘basaltic elements’, leading to a harzburgitic source which was enriched by an early LREE contribution during the stabilization of the Archaean to Proterozoic Aldan Shield. It is further suggested that the Mesozoic northwesterly directed subduction of the Ochotsk-Chukotsk belt influenced the subcontinental lithosphere underneath the Aldan Shield, leading to the observed subduction-related signature of the Yakokut lamproites.

Volcanic-hosted advanced argillic alteration on Barton Peninsula comprises an assemblage of chalcedonic silica, alunite family minerals, pyrophyllite, pyrite, native sulphur, zunyite and rutile, characteristic of an acid sulphate-type epithermal system. The minerals minamiite, (Na0.36Ca0.27K0.1□0.27)Al3(SO4)2(OH)6, and zunyite, Al13Si5O20(OH,F)18Cl, are reported at this locality, and in Antarctica, for the first time. The WNW-striking, 1 km-long zone of alteration is hosted by early Tertiary andesitic rocks and contained in a 1.5 km-wide depression, rimmed by an arcuate ridge, probably representing a volcanic crater or small caldera structure.

Stability relations of minerals in the advanced argillic alteration zone indicate alteration took place under acidic conditions in the near-surface environment. Mineralogical and textural evidence also suggest alteration occurred in a magmatic hydrothermal system, possibly with a magmatic steam component, rather than in a supergene or steam-heated environment.

The Krymka chondrite contains an exotic graphite-bearing fragment that appears to be of a new type of material added to unequilibrated LL-chondrite during agglomeration on the surface of the parent body. The fine-granular texture without chondrules, two morphological groups of graphite crystals which differ in size and occurence, high content of troilite (11.3 vol.%), the high Ni (55.5–66.6 wt.%) and Co (1.59–2.87 wt.%) contents of the taenite and absence of kamacite, the presence of F-apatite, which is rare for meteorites but common for lunar and terrestrial igneous rocks, are the main features of the fragment.

The mineralogy and texture indicate: (1) the fragment probably formed by crystallization from a highly reduced silicate melt, which had been enriched in carbon; 2) the subsequent metal sulphidization lowered its abundance and resulted in the formation of troilite and the compositional features of the residual metal; (3) terrestrial weathering of an exotic fragment and the host part of the chondrite produced iron hydroxides, pentlandite and quite possibly magnetite.

Palladium-bearing minerals from the Cauê iron mine, Itabira District, Minas Gerais, Brazil, are found in gold-rich jacutinga, a hydrothermally-altered Lake Superior-type carbonate-bearing oxide facies iron-formation. Palladium occurs as: native palladium with trace contents of Au, Fe and Cu; palladseite ((Pd,Cu,Hg)17Se15), which was found in the core of a grain of palladium; palladium–copper oxide ((Pd,Cu)O); and arsenopalladinite (Pd8(As,Sb)3), with inclusions of palladium–copper oxide. The palladium and palladium–copper oxide grains are coated with films of gold and commonly do not exceed 100 µm in width. These palladium minerals occur in hematite bands and in boudinaged bands of quartz and white phyllosilicate parallel to the S1 mylonitic foliation. Palladium-copper oxide also occurs as inclusions in gold grains which are strongly to weakly stretched parallel to S1.

Palladium mineralization is interpreted as synchronous with intense D1 shearing and contemporaneous with the peak of thermal metamorphism. At high oxygen fugacities and high temperatures (up to 600°C), Pd may have been transported as chloride complexes and deposited following changes in pH caused by mineralizing fluids reacting with jacutinga. Deposition may also have been prompted by the formation of insoluble selenide and arsenide–antimonide minerals and by the dilution of C1 concentrations in the mineralizing fluid. Textural studies, and the zonation observed in palladium and other hydrothermal minerals, suggest that oscillations in the physico-chemical conditions of hydrothermal fluids occurred during the mineralizing event.

A sapphire, zircon and magnetite-bearing xenolith from Khao Wua, near Chanthaburi in Thailand, conclusively demonstrates a common origin for the sapphire, zircon and magnetite found in alluvial deposits in the Chanthaburi gem fields. The original aluminium- and titanium-rich octahedral magnetite crystal in the xenolith exsolved into hercynite, magnetite and hematite during cooling. It includes minor anhedral jarosite–alunite, possibly originating as an iron-sulphide-rich immiscible liquid. Uranium-lead isotope dating of zircon in the xenolith gives an age of 1–2 (± <1) million years (Ma). This falls within fission track ages for alluvial zircons (2.57 ± 0.20 Ma) from the Chanthaburi—Trat gem fields and within the potassium-argon ages of 0.44 to 3.0 Ma for the alkali basaltic volcanism in the Chanthaburi Province. These data suggest a common origin for sapphire, zircon and magnetite, and link them with the processes involved in alkali basaltic magma generation. The high iron and zirconium, low magnesium, and the inferred sulphides suggest pegmatite-like crystallization in an incompatible-element enriched, silica-poor magma (partial melt or fractionation product) in the deep crust or upper mantle. Etch features on exposed surfaces of the xenolith indicate that it was transported out of its equilibrium environment by the rise of later magma.

MnxZn(1−x)CO3 solid-solutions were prepared at 5°C by precipitation from metal-bearing bicarbonate solutions. The solids were identified by X-ray powder diffraction and infrared spectroscopy. Zn2+ ions substitute extensively for Mn2+ ions in the crystal lattice of anhydrous rhombohedral carbonates. Throughout the 24 h during which the experiments were conducted, the aqueous solutions remained undersaturated with respect to pure oxides, sulphates, hydroxides and hydroxysulphates. The solutions, however, were supersaturated with MnxZn(1−x)CO3 of any given composition. Besides the anhydrous rhombohedral carbonates, Zn4(OH)2(CO3)3·4H2O was precipitated from an aqueous solution with initially high Zn2+ concentration. The negative logarithm of the solubility product of Zn4(OH)2(CO3)3·4H2O was estimated theoretically to be 43.9 (25°C). Remaining saturation with respect to Zn4(OH)2(CO3)3·4H2O was calculated accordingly. The suggestion is made that hydrated zinc hydroxycarbonate is metastable under the experimental conditions used here, but that it should transform into anhydrous carbonates.

Ilvaite is sparsely disseminated in a serpentinized plagioclase wehrlite of the Asama igneous complex that underwent the Sambagawa regional metamorphism of pumpellyite-actinolite to greenschist facies. Ilvaite in the Asama complex is monoclinic (a = 13.019(5), b = 8.808(2), c = 5.850(4) Å, β = 90.19(4)°), and its composition is similar to the ideal end-member composition (). Ilvaite occurs in mats of serpentine (chrysotile); it probably formed during serpentinization, which might have accompanied the Sambagawa metamorphism. The associated secondary minerals include salitic clinopyroxene, magnetite and andradite. The ilvaite-free mineral assemblage that formed during the serpentinization is usually serpentine-clinopyroxene-magnetite, which is widespread in the complex. The phase relations between coexisting minerals suggest that the conditions during the formation of the ilvaite-bearing assemblage were reducing when compared to those of the assemblage serpentine-clinopyroxene-magnetite. The reducing conditions during the ilvaite formation were presumably brought about by hydrogen gas that1 was generated during the serpentinization of olivine.

Detailed microprobe and modal data for a sample of layered, garnetiferous, quartzose paragneiss reveal significant differences in garnet-biotite Mg-Fe distribution coefficients (Kd) — and hence paleotemperatures — determined for leucocratic (modal Grt+Bt<25 vol.%) and mesocratic (Grt+Bt> 25 vol.%) layers. In leucocratic layers, lnKd determined from both the core and rim compositions of minerals shows a range of values that varies sympathetically with the absolute amount of garnet and biotite, and, as demonstrated in other studies, inversely with the distance separating both minerals. Due to the small size (<2 mm) of garnets, which facilitated diffusional re-equilibration during cooling from peak metamorphic temperature, lnKd does not correlate to modal Bt/Grt ratios. The largest garnets, which occur in mesocratic layers, nonetheless tend to preserve the most pronounced (retrograde) zoning patterns (i.e. rimward increase in Fe/Mg), consequently mineral core composition lnKd values correlate with grain diameter except where garnets contain abundant biotite inclusions. The highest Grt-Bt temperatures (∼700°C are recorded by: (1) the composition of relatively widely-separated (>0.3 mm) grains in highly leucocratic layers; and (2) the core compositions of relatively large (>1 mm), inclusion-free grains in mesocratic layers. More closely spaced garnets and biotites in leucocratic layers, and small grains in mesocratic layers, give a range of temperatures intermediate between Tmax and diffusional blocking temperatures (∼ 560°C) recorded by the rim compositions of contiguous grains.

Scanning Electron Microscopy and Transmission Electron Microscopy show that normal, slightly turbid alkali feldspars from many plutonic rocks contain high concentrations of micropores, from ∼1 µm to a few nm in length, typically 0.1 µm. There may be 109 pores mm−3 and porosities as high as 4.75 vol.% have been observed, although ∼1% is typical. Only ‘pristine’ feldspars, which are dark coloured when seen in the massive rock, such as in larvikite and some rapakivi granites, are almost devoid of pores. Weathering enlarges prexisting pores and exploits sub-regularly spaced edge dislocations which occur in semicoherent microperthites, but the underlying textures which lead to skeletal grains in soils are inherited from the high temperature protolith. Most pores are devoid of solid inclusions, but a variety of solid particles has been found. Although the presence of fluid in pores cannot usually be demonstrated directly, crushing experiments have shown that Ar and halogens reside in fluids. Some pores are ‘negative crystals’, often with re-entrants defined by the {110} Adularia habit, while others have curved surfaces often tapering to thin, cusp-shaped apices. The variable shape of pores accounts for the ability of some pores to retain fluid although the texture is elsewhere micropermeable, as shown by 18O exchange experiments.

Apart from rare, primary pores in pristine feldspar, pore development is accompanied by profound recrystallization of the surrounding microtexture, with partial loss of coherency in cryptoperthites. This leads to marked ‘deuteric coarsening’ forming patch and vein perthite, and replacement of ‘tweed’ orthoclase by twinned microcline. The Ab- and Or-rich phases in patch perthite are made up of discrete subgrains and the cuspate pores often develop at triple-junctions between them. Coarsened lamellar and vein perthites are composed of microporous subgrain textures. These ‘unzipping’ reactions result from fluid-feldspar interactions, at T <450°C in hypersolvus syenites and T < 350°C in a subsolvus granites, and are driven by elastic strain-energy in coherent cryptoperthites and in tweed textures. Further textural change may continue to surface temperatures. In salic igneous rocks there is a general connection between turbidity and the type of mafic mineral present; pristine alkali feldspars occur in salic igneous rocks with a preponderance of anhydrous mafic phases.

Because alkali feldspar is so abundant (and larger, 10 μm pores have previously been described in plagioclase), intracrystal porosity is a non-trivial feature of a large volume of the middle and upper crust. The importance of pores in the following fields is discussed: 39Ar/40Ar dating and ‘thermochronometry’; oxygen exchange; Rb and Sr diffusion; weathering; experimental low-temperature dissolution; development of secondary porosity and diagenetic albitization; leachable sources of metals; nuclear waste isolation; deformation; seismic anisotropy; electrical conductivity. Important questions concern the temperature range of the development of the textures and their stability during burial and transport into the deeper crust.

New chemical analyses, electron and X-ray powder diffraction data, and comparison with gyrolite and reyerite show that tungusite has the ideal formula , symmetry P and a = 9.714(9), b = 9.721(9), c = 22.09(3), α = 90.13(1)°, β = 98.3(2)°, γ = 120.0(1)°, Z = 1. A structural model for tungusite is derived by splitting the double tetrahedral layer of reyerite and inserting a trioctahedral X sheet which is ideally occupied by Fe2+. Polytypism phenomena due to different relative positions between tetrahedral and X sheets are discussed. A substitutional solid solution represented by the formula [Ca14(OH)8]Si24−yAlyO60[NaxM9−(x+z)□z(OH)14−(x+y+2z)·(x+y+2z)H2O] includes tungusite (x = y = z = 0, M = Fe2+ and gyrolite (x = 1, y = 1, z = 6, M = Ca).

Kusachiite, CuBi2O4, has been found in a calcite vein cutting gehlenite-spurrite skarns at Fuka, Okayama Prefecture. It is associated with calcite, henmilite, sillenite, bakerite, tenolite, bultfonteinite, apophyllite, cuspidine and thaumasite. Kusachiite occurs as prismatic crystals or globular aggregates of platy crystals. It is black, opaque with a metallic lustre. Kusachiite is tetragonal with space group P4/ncc, a = 8.511(2), c = 5.823(2) Å, Z = 4. The strongest lines in the X-ray powder pattern [d in Å (I)(hkl)] are 3.191 (100)(211), 2.695 (18)(310), 1.947 (18)(411), 4.26 (17)(200), 2.913 (16)(002), 2.404 (13)(202), 1.728 (12)(213), and 1.652 (9)(332). The Mohs hardness is 4.5, and the density is 8.5(3) g/cm3 (meas.) and 8.64 g/cm3 (calc.). Cleavage is perfect on {110}. Six electron probe analyses gave the following mean values CuO 13.91, Bi2O3 86.00 and total 99.91 in wt.%. The empirical formula calculated on the basis of O = 4 is Cu0.960Bi2.027O4 with the simplified formula CuBi2O4.

Takedaite, Ca3B2O6, has been found in crystalline limestone near gehlenite−spurrite skarns at Fuka, Okayama Prefecture. It occurs as aggregates of granular crystals up to 0.8 mm long and 0.3 mm wide. The mineral is associated with nifontovite, olshanskyite, pentahydroborite, frolovite, sibirskite, calcite and an unidentified mineral, is white or pale gray, and has a vitreous luster. Takedaite is trigonal with space group of Rc, a = 8.638(1), c = 11.850(2)Å, Z = 6. The strongest lines in the X-ray powder pattern [d in A(I)(hkl)] are 2.915(100)(113), 1.895(75)(223), 2.756(61)(104), 2.493(44)(300), 2.044(21) (214,131), 2.160(19)(220), 1.976(18)(006), 1.549(12)(306). The Vickers microhardness is 478 kg mm−2 and the Mohs hardness 4.5. The density is 3.10(2) g cm−3 (meas.) and 3.11 g cm−3 (calc.). Wet chemical analyses give the values CaO 71.13%, B2O3 28.41%, ig. loss 0.14%, and total 99.68%. The empirical formula calculated on the basis of O = 6 is Ca3.053B1.965O6, with the simplified formula of Ca3B2O6.

Wupatkiite (Co,Mg,Ni)Al2(SO4)4.22H2O is a new member of the halotrichite group. It occurs 8 miles ESE of Gray Mountain, Arizona, near the prehistoric pueblo dwelling Wupatki. It occurs as cross-fibre veinlets with fibres up to 8mm long. Colour: empire rose (RHS48C), streak white, H. = 1 ½. G = 1.92, D(calc) = 1.87g/cm3. Nonpleochroic with α = 1.477, γ = 1.484, Z^fibre axis = 12°. Wet chemistry gave MgO 1.63, CaO 0.10, MnO 0.17, FeO 0.15, NiO 0.52, CuO 0.12, CoO 3.41, Al2O3 11.30, SO3 35.97, H2O 42.26 (total 95.63%); rem. = montmorillonite and quartz. Parameters refinedo from the powder pattern are close to those of halotrichite. Wupatkiite is monoclinic P21/c with a = 6.189 Å, b = 24.23 Å, c = 21.20 Å, β = 100.33°. Strongest lines are 4.790, 100 (024); 4.295, 27 (140); 3.945, 26 (025); 3.768, 33 (062); 3.494, 92 (124, 063).