Some of the physical, chemical and mineralogical characteristics of Portland cement and related materials relevant to nuclear waste immobilization are defined. The ability to condition and maintain a high aqueous pH is undoubtedly the most important factor: it precipitates many species as hydrous oxides or hydroxides. However, in the longer term, many species – cationic as well as anionic – react with one or more cement components forming solubility-limiting phases. Progress on characterization of these phases is outlined. Many of the host phases have natural equivalents and this gives comfort in respect of their likely persistence over geological time. The emerging picture of immobilization in cement suggests that cement compositions can be tailored in terms of pH, Eh and internal chemistry so as to maximize immobilization potential. Nickel, uranium and chromium and chloride are used as examples.

An inclusion of corundum (ruby) was found in a clinopyroxene xenocryst in alkali basalt from the late-Cenozoic Chanthaburi-Trat volcanics of eastern Thailand. The clinopyroxene is fairly sodic, highly aluminous and magnesian (0.12–0.14 Na, 0.31–0.33 AlIV and 0.36–0.40 AlVI per 6(O), and Mg/(Mg+Fe2+) > 0.9)) and is chemically similar to clinopyroxene inclusions in rubies from nearby alluvial gem deposits, suggesting a common origin for the two types of occurrence. Sapphirine (Mg/(Mg+Fe2+) = 0.91–0.94) and garnet (py56–67alm11–18grs18–23) also occur as inclusions in alluvial rubies. Thermodynamic calculation of the equilibrium 2 di + 2 crn = 2 cats + en constrains the temperatures of clinopyroxene + corundum crystallization to between 800 and 1150 ± 100°C. Use of other equilibria as stability limits places the pressures of crystallization between 10 and 25 kbar, implying depths of between 35 and 88 km. The most Fe-rich clinopyroxene crystallized at a pressure in the lower part of the range. The pyropic garnet inclusions in corundum crystallized at pressures of >18 kbar (i.e. at depths > ~63 km).

The xenocrystic clinopyroxene could have coexisted in equilibrium with garnet of similar composition to the observed inclusions at the deduced temperatures of crystallization. The rubies probably crystallized in rocks of mafic composition, i.e. garnet-clinopyroxenites or garnet-pyriclasites, within the upper mantle.

Rengeite, Sr4ZrTi4Si4O22, is a new member of the perrierite–chevkinite group found in the jades from the Itoigawa-Ohmi district, central Japan. It is monoclinic, P21/a, a = 13.97(1), b = 5.675(7), c = 11.98(1)Å, β = 114.26(8)°, V = 866 Å3 and Z = 2. The six strongest lines in the X-ray powder diffraction pattern are 3.12 (s) (40-3), 3.05 (vvs) (31-3), 2.99 (vs) (311), 2.84 (s) (020), 2.74 (s) (004), 2.20 (s) (31-5). Electron microprobe analysis gave SiO2 22.58, TiO2 29.88, ZrO2 9.49, Nb2O5 0.24, Ta2O5 0.07, Al2O3 0.20, FeO 0.10, CaO 0.43, SrO 34.32, BaO 0.13, La2O3 0.00, Ce2O3 0.38, Pr2O3 0.10, Nd2O3 0.29, Sm2O3 0.04, total 98.25 wt.%, corresponding to (Sr3.62Ca0.08Ce0.03Nd0.02Ba0.01Pr0.01)∑3.76 (Zr0.84Ti0.09Al0.04Fe0.02Nb0.02)∑1.01Ti4.00Si4.11O22 on the basis of O = 22. The unitcell parameters and chemical composition imply that rengeite is the Sr and Zr-analogue of perrierite or high-β analogue of strontiochevkinite. It is transparent, dark brown with adamantine lustre. Its streak is pale greenish brown, and no cleavage was observed. The hardness is VHN100 606–698 kg mm−2 (Mohs 5–5.5). The calculated density is 4.12 g cm−3. It is strongly pleochroic from pale green to pale greenish brown where the REE contents are <1 wt.% and pale violet to greenish brown where the REE contents are between 3 and 10 wt.%. It occurs as anhedral grains in close association with titanite, zircon and tausonite in a pebble of blue titanian omphacite-jadeite rock from the seashore of Oyashirazu, Ohmi Town, in a boulder of lavender-coloured Ti-bearing jadeitite from the bed of the Kotaki-gawa river, Itoigawa City, and in a boulder of green jade from the bed of the Hime-kawa river, Itoigawa City, Niigata Prefecture, central Japan. Rengeite is considered to have crystallized by interaction between pre-existing minerals (rutile, anatase, titanite and zircon) and Sr-rich metamorphic fluid during later stage activity of high-P/T metamorphism. The name is for Mt. Renge near the locality and the Renge metamorphic belt where jadeitite deposits are found.

The Raman spectrum of holmquistite, a Li-containing orthorhombic amphibole from Bessemer City, USA has been measured. The OH-stretching region is characterized by bands at 3661, 3646, 3634 and 3614 cm−1 assigned to 3 Mg–OH, 2 Mg + Fe2+–OH, Mg + 2Fe2+–OH and 3 Fe2+–OH, respectively. These Mg and Fe2+ cations are located at the M1 and M3 sites and have a Fe2+/(Fe2+ + Mg) ratio of 0.35. The 960–1110 cm−1 region represents the antisymmetric Si–O–Si and O–Si–O stretching vibrations. For holmquistite, strong bands are observed around 1022 and 1085 cm−1 with a shoulder at 1127 cm−1 and minor bands at 1045 and 1102 cm−1. In the region 650–800 cm−1 bands are observed at 679, 753 and 791 cm−1 with a minor band around 694 cm−1 attributed to the symmetrical Si–O–Si and Si–O vibrations. The region below 625 cm−1 is characterized by 14 vibrations related to the deformation modes of the silicate double chain and vibrations involving Mg, Fe, Al and Li in the various M sites. The 502 cm−1 band is a Li–O deformation mode while the 456, 551 and 565 cm−1 bands are Al–O deformation modes.

Crystals of the compound Na4(UO2)(CO3)3 have been synthesized and the structure has been solved. It is trigonal with a= 9.3417(6), c = 12.824(1) Å, V = 969.2(1) Å3, space group Pc1 and Z = 4. The structure was refined on the basis of F2 (wR2 = 4.2%) for all unique data collected using Mo-Kα X-radiation and a CCD-based detector. The final R1 was 2.0%, calculated for 534 unique observed (Fo ≥ 4σF) reflections, and the goodness-of-fit (S) was 0.91. The structure contains a uranyl tricarbonate cluster composed of a uranyl hexagonal bipyramid that shares three equatorial edges with CO3 triangles. The uranyl tricarbonate clusters are connected through NaO6 and NaO5 polyhedra, forming a heteropolyhedral framework structure. This compound may be related to a uranyl carbonate phase with the same composition which has been reported as an alteration phase on the surface of Chernobyl ‘lava’, and as a mineral in the Jachymov ore district, Czech Republic.

Air pollution control (APC) facilities at waste incinerator plants produce large quantities of solid residues rich in salts and heavy metals. Heavy metals are readily released to water from the residues and it has, therefore, been found suitable to apply a rapid co-precipitation/adsorption process as a means to immobilize the toxic elements. In the ‘Ferrox process’, this immobilization is based on co-precipitation with an Fe(III) oxide formed by oxidation of Fe(II) by air in an aqueous slurry with the APC residue at alkaline pH. In this work we have undertaken a Mössbauer spectroscopy study of the Fe oxide phase formed by precipitation at room temperature and of the oxides present after heating to 600 and 900°C. The only Fe oxide observed in the Ferrox product at room temperature is a very poorly crystalline ferrihydrite. Analytical transmission electron microscopy showed that the main elements associated with the ferrihydrite are Si and Ca. Following heating to 600°C the oxide is still characterized as an amorphous Fe oxide, and it is probable that Si associated with the ferrihydrite is decisive in preventing crystallization. After the 900°C treatment a transformation into defect maghemite is observed. Reducing gases produced from carbon in the samples probably induces this transformation. It eases, thus, the reduction of Fe(III) and the consequent formation of magnetite that eventually oxidizes to maghemite during cooling in air.

Woodallite is a new Cr-rich member of the hydrotalcite group from the large, low-grade Mount Keith nickel deposit, in the northeastern Goldfields district of Western Australia. Woodallite occurs as whorls and clusters of minute platelets up to 6 mm across in lizardite+brucite-altered dunite. Individual platelets are typically 10–100 µm in maximum dimension and are often curved. Associated minerals include chromite, lizardite, iowaite, pentlandite, magnetite, tochilinite and brucite. Electron microprobe analysis gave: Mg 25.90 wt.%; Cr 10.81; Fe 4.86; Al 0.68; Cl 9.89; S 0.03; Si 0.01; Ni 0.01; Na 0.01, yielding (after correction for loss of volatiles) an empirical formula of Mg6.19(Cr1.21Fe0.51Al0.15)∑1.87(OH)16[Cl1.62(CO3)0.17(SO4)0.01]·4H2O, by analogy with the hydrotalcite group. The simplified formula is Mg6Cr2(OH)16Cl2·4H2O. Combined thermogravimetric analysis and mass spectroscopy showed a two-stage weight loss of 12.7% and 27.3% occurring over the ranges 25–300°C and 300–660°C, respectively. The first weight loss is attributed to loss of interlayer water, chlorine-bearing species (e.g. HCl) and some CO2, the second to loss of hydroxide water, remaining CO2 and Cl species. The mineral is deep magenta to purple in colour, transparent, with a resinous to waxy lustre, and a perfect basal {0001} cleavage. Woodallite has a Mohs hardness of 1.5–2, and a pale-pink to white streak. The strongest lines in the X-ray powder pattern are [dobs (Iobs) (hkl)] 8.037 (100) (003); 4.021 (48) (006); 2.679 (1) (009); 2.624 (3) (012); 2.349 (5) (015); 2.007 (6) (0,0,12); 1.698 (2) (0,1,11); 1.524 (2) (23). These lines were indexed on a hexagonal cell with a = 3.103(2), c = 24.111(24)Å, V = 201.14 Å3 and Z = 3/8. The new mineral is isostructural with the hydrotalcite group and has space group Rm. The measured density is 2.062 gm/cm3. Woodallite is uniaxial negative with ω = 1.555 and ε = 1.535 (white light); pleochroism is distinct from violet to pinkish lilac. Woodallite forms as a result of hydrothermal alteration of primary magmatic chromite by Clrich solutions at temperatures <320°C. Relict chromite fragments are frequently present in the whorls, and associated magnetite is altered extensively to iowaite. The mineral is named after Roy Woodall, eminent Australian industry geologist.

A magmatic calcic amphibole (M4Ca≥1.50) characterized by large Sr and F contents (SrO>1 wt.%, F>2.5 wt.%) is described. According to the crystal-chemical formula, the amphibole can be classified as a strontian fluoro-magnesiohastingsite and the presence of Sr cations in the A sites is suggested. The amphibole occurs in the groundmass of ultrapotassic lavas from the Alban Hills Volcanic District (Central Italy). This peculiar chemical composition is due to the lavas' groundmass compositional trend occurring under low silica-activity conditions. We suggest that the occurrence of F amphiboles allows us to consider the Alban Hills Volcanic District magmas to be as rich in F as other ultrapotassic magmas.

In order to investigate the range of the solid solution series in herzenbergite-teallite minerals, samples of different composition were synthesized. Herzenbergite-teallite minerals were synthesized by an evacuated silica glass tube method at 700°C. A linear relationship between cell dimensions, a, b and c and composition is established. Extension of solid solution to the Pb-rich portion of the system PbS-SnS is limited; the solid solution area is between Pb1.060Sn0.940S2 and SnS at 700°C. Teallite coexisting with galena was also synthesized by hydrothermal recrystallization at 300, 400 and 450°C. The compositions of teallite are Pb1.140Sn0.860S2 at 300°C, Pb1.114Sn0.886S2 at 400°C, and Pb1.124Sn0.876S2 at 450°C, respectively. Their compositions shift towards the PbS end-member from stoichiometric teallite. The cell dimensions of teallite, which was synthesized hydrothermally, follow the linear relationship between cell dimensions and composition established at 700°C.

In order to assess the role played by sheet silicates in controlling base metal distribution, the mineralogy of the <2 µm fraction of waste material, surface soils, and stream sediments was investigated in the surroundings of a pyrite-chalcopyrite mine area in northern Italy. The results indicate that smectite is very abundant in the <2 µm fraction of the tailings, and it exerts an effective control on the concentrations of Zn, Ni (and Cu). Normal soils and sediments are characterized by interstratified illite-smectite and by lower base metal concentrations. Away from the mine area, smectite decreases in the stream sediments, and chlorite becomes more important in controlling base metal distribution.

Ni, Cr, Cu and Co increase with chlorite and talc, but are depleted in the <2 µm fraction compared to coarser fractions in the stream sediments, because the sand–silt fraction of sediments concentrates ophiolitic fragments, variably enriched in ores. A mechanical dispersion of chlorite is probably the controlling factor. Zinc displays a systematic enrichment in the clay fraction of waste material and in the stream sediments but the main mineral carrier is not identified.

Idioblastic, mm-scale brookite is reported from SiO2-Ba-Fe-rich metasomatic rocks from the carbonatitic Gross Brukkaros Volcanic Field, Southern Namibia. Electron probe microanalysis shows significant concentrations of Nb (12–17 wt.% Nb2O5), coupled with Fe, substituting for Ti in the structure. Calculation of the analytical data indicates evolving Fe2+/(Fe2++Fe3+) ratios during crystallization and two distinct substitution mechanisms in operation: 2Ti4+ ⇋ Nb5+ + Fe3+ and 3Ti4+ ⇋ 2Nb5+ + Fe2+. The compositional patterns observed are explained in terms of initial growth in an environment which evolved from oxidizing to reducing. The outermost 10 µm rims of the crystals are characterized by oxidizing conditions, resulting from a subsequent metasomatic overprint.

The pseudomorphic replacement of glass shards by zeolite minerals is a common feature of volcanoclastic sediments. In the majority of cases the initial stage of this reaction is the alteration of the glass surface to a clay mineral or celadonite after which the bulk of the glass is altered to zeolite. This replacement feature is seen particularly well in glass of rhyolitic composition; the zeolite mineral usually being clinoptilolite. Volcanoclastic rocks of Oligocene age exposed in the Rhodope Massif, Bulgaria offered an opportunity to study this reaction experimentally as rocks containing unaltered glass shards are known to be close stratigraphic equivalents of zeolitized tuffs and in this respect are considered to be precursor rocks. Low-temperature hydrothermal reactions conducted on the unaltered glass, which had been clay coated in the laboratory, demonstrates the importance of the clay-glass interface. An hypothesis is put forward to explain this type of zeolitization process and a distinction is drawn between these rocks and other sediments in which zeolite minerals form from volcanic glass without the presence of a clay interface.

In hypabyssal and crater-facies kimberlites of the Lac de Gras kimberlite field, perovskite occurs as reaction-induced rims on earlier-crystallized Ti-bearing minerals (magnesian ilmenite and priderite), inclusions in atoll spinels and discrete crystals in a serpentine-calcite mesostasis. The mineral is associated with spinels, apatite, monticellite, phlogopite, baryte, Fe-Ni sulphides, ilmenite, diopside and zircon. Uncommon accessory phases found in an assemblage with perovskite include titanite, monazite- (Ce), witherite, strontium-apatite, khibinskite, djerfisherite, wollastonite, pectolite, suolunite, hydroxyapophyllite and bultfonteinite. Three types of perovskite can be distinguished on the basis of composition: (I) REE-Nb-Al-poor perovskite with relatively high Sr and K contents (up to 2.2 and 0.6 wt.% oxides, respectively) occurring as mantles on priderite and inclusions in atoll spinels; (II) perovskite with elevated Al, Fe, Nb and LREE (up to 1.4, 8.3, 9.1 and 17.0 wt.% oxides, respectively) found as discrete crystals and rims on macrocrystic ilmenite; (III) perovskite significantly enriched in Na, Sr, Nb and LREE (up to 3.3, 3.4, 13.0 and 22.6 wt.% oxides, respectively) found as rims on perovskite I and II. The overwhelming majority of perovskite is represented by discrete crystals of type II. In some occurrences, this type of perovskite also has high Th contents (up to 5.5 wt.% ThO2) and Zr contents (up to 3.7 wt.% ZrO2). Textural evidence indicates that perovskite shows an overall evolutionary trend from the most primitive type I towards type III showing the highest Na, Nb and LREE contents. Perovskite of type I probably crystallized under relatively high pressures prior to the precipitation of MUM spinels. Perovskite II crystallized after magnesiochromite, pleonaste and MUM (magnesian ulvöspinel-magnetite) spinels, under increasing fO2. The most compositionally evolved type III formed during near-solidus re-equilibration of the earlier-crystallized perovskite. The compositional variation of the Lac de Gras perovskite can be adequately characterized in terms of five major end-members: CaTiO3 (perovskite), CeFeO3, NaNbO3 (lueshite), Na0.5LREE0.5TiO3 (loparite), and CaFe0.5Nb0.5O3 (latrappite).

The ultrastructures of parisite-(Ce) from a rare-earth mineral deposit of Sichuan Province, southwest China, have been observed and investigated by selected area electron diffraction (SAED) and high resolution electron microscopy (HREM). Six new polytypes 4H, 10H, 16H, 18R, 24R and 30R were determined in parisite-(Ce), as were their crystal structure types, subcell (a′c‴, a′c″, a′c′) and supercell (ac) parameters, reflection conditions, polytype features and probable space groups. The HREM studies revealed the complex polytypism in parisite-(Ce) whereby the six new polytypes, formed by long-period ordered stacking, always coexist with the common polytype parisite-(Ce)-6R by syntaxy and thus constitute the complex microstructural ‘syntactic polycrystals’, the host of which is the polytype parisite-(Ce)-6R.

Brunogeierite, Fe2GeO4, a = 8.4127(7) Å, V = 595.4(1) Å3, is a rare germanate spinel from Tsumeb, Namibia. Its structure has been refined to an R index of 2.2%. The oxygen parameter, u, is 0.2466(1), indicating nearly ideal cubic close-packing of oxygen atoms. There is exact agreement between the observed a unit-cell dimension and that calculated from the observed Ge–O and Fe–O bond lengths. The cations Ge and Fe are fully ordered at tetrahedral (A) and octahedral (B) sites, respectively, in keeping with synthetic germanate spinels, all of which are fully-ordered normal spinels.