New chemical analyses of roeblingite from Franklin, New Jersey, and Långban, Sweden, are presented. The average composition of Franklin roeblingite is SiO2 24.9, CaO 23.8, SrO 2.4. MnO 2.4, PbO 30.2 SO3 10.4, H2O 6.13%, Sum = 100.23%. The data support space group C2/m and suggest the formula is (Ca,Sr)12 (Mn,Ca)2Pb4(SO4)4Si12O28(OH)20, if there is ordering on the site of rank 2.

Dervillite, As2AsS2, has been found in a sample from the Lengenbach quarry in the Binn Valley, Valais, Switzerland. It occurs as very rare crystals up to 200 μm across on jordanite. Dervillite is opaque with a metallic lustre and shows a dark brown streak. The structure is monoclinic, space group Pc, with a = 9.6155(7), b = 12.9331(8), c = 6.8616(5) A ˚ , b = 99.352(8)º, V = 842.0(1) Å3 and Z = 8. In the crystal structure [R1 = 0.060 for 2370 reflections with I > 2σ(I)], silver adopts various coordinations extending from quasi linear to quasi tetrahedral whereas arsenic forms very peculiar crystal-chemical environments, such as As(S2As) and As(S2AsAg). Such metalloid–metalloid or metal–metalloid bonds account for the apparent charge imbalance observed in the chemical formula.

Tausoare Cave is renowned in Romania for its gypsum and mirabilite speleothems. Of interest are the white crystalline speleothems formed on the floor of the ‘Sala de Mese’ (Dining Room) that were previously described as consisting of mirabilite. The samples we collected reveal crystals of two different habits. One shows the characteristic mirabilite fibrous crystals (cotton-like speleothem) while the other formed bladed and short prismatic crystals which comprise the delicate ‘cave flowers’. The mineral association was characterized by means of X-ray analysis, scanning electron microscopy and electron microprobe. Beside thenardite (dehydration product of mirabilite) we also identified three sulphate minerals: leonite [K2Mg(SO4)2·4H2O], syngenite [K2Ca(SO4)2·H2O] and konyaite [Na2Mg(SO4)2·5H2O]. Of these, leonite and konyaite have never been reported in a cave environment. This paper describes the mineralogy of this particular sulphate deposit and offers some viewpoints on the crystallogenesis.

Detailed chemical analyses of different portions of laboratory-grown sector-zoned clinopyroxene been provided by Skulski et al. (1994). These data have been plotted here in PC-IR diagrams results indicate equilibrium crystallization and protosite control of element selection.

Single crystals of Sr feldspar (SrAl2Si2O8, space group: I2/c) were treated isothermally in the temperature range between 1410 and 1640°C, in order to determinate the evolution of the Al,Si configurations at equilibrium with thermal treatments. X-ray intensity data collection and structural refinement were performed on the quenched crystals. Significant modifications were observed in the average tetrahedral distances and therefore in Qod values.

Two different series of thermal treatments were performed: (1) a crystal of ordered Sr feldspar (Qod= 0.85) was progressively disordered at 1560°C (Qod = 0.82), at 1610°C (Qod = 0.74) and at 1640°C (Qod = 0.69); (2) another crystal with Qod = 0.72 (obtained by annealing a glass at T =1625°C), was ordered at T = 1600° (Qod = 0.75).

As already observed in anorthite quenched from 1530°C (Qod = 0.78), also in Sr feldspar, annealing near Tmelt, caused significant disorder in the Al-Si configuration (Qod = 0.69).

Observations by transmission electron microscopy show an increase in the average size of the i-type antiphase domains up to 5000Å in the samples quenched from 1640°C, in comparison with samples annealed at 1450°C (∼ 2000 Å). The modifications observed in the Al,Si configurations are due to intradomain disorder.

Rock samples from the various metabasic hornfelses of the Land's End granite aureole were analysed for major elements by X-ray fluorescence analysis and for rare-earth elements (REE) by instrumental neutron activation analysis (INAA). The REE patterns of the unaltered dolerites of the area seem to be analogous to those of the alkali basalts, taking into account a slight mobilization of the light REE during low-grade metamorphism.

The REE content of the metabasic rocks of the aureole has increased relative to that of the unaltered dolerites due to the introduction of REE, along with K, from the granite by the action of hydrothermal solutions. The parallel increase in REE with the increase in K is demonstrated.

The metasomatic hornfelses of igneous origin form two groups showing slightly different REE patterns and different rates of increase in REE content. The REE patterns of the two groups show a Eu anomaly increasing with the increase in REE content for the first group and decreasing with the increase in REE content for the second group, A qualitative model of the distribution of the REE in the metabasic aureole rocks is given.

Studies of the U decay series (238U-234U-230Th) have been carried out on samples from unaltered bedrock and highly altered fracture/crush zones from drillcore Km3 (Kamlunge test-site). The fracture zones are characterized by abundant iron oxide coatings (hematite and hydroxy iron oxides) resulting from the passage of hydrothermal solutions coeval with the Lina granite intrusion. Enrichments of U and Th, thought to be due to co-precipitation (or preferential sorption) processes together with the iron-oxides, are also present.

The isotopic results show that out of a total of twelve rock samples measured, six indicate isotopic disequilibrium mostly due to unequal depletions of 234U and 238U; one near-surface sample indicated some minor assimilation of U. The major fracture zones generally indicate removal of total U. This has resulted from interaction with groundwaters which are still marginally oxidizing, even at depths of 375 m.

Isotopic disequilibrium has occurred within recent geological times, i.e. during the last 0.5 Ma as imposed by the half-lives of 234U and 230Th. In terms of radioactive disposal considerations, the results are important in that: (1) the investigated bedrock environment (100–500 m) is generally reducing; however (2) there is some evidence to indicate that rock/water interactions, leading to the removal of total U, have resulted from the presence of less reducing groundwaters within those large-scale fracture/crush zones which intersect the bedrock surface.

Yugawaralites from two localities in Japan consist of growth sectors with variable 2V values and extinction angles. The optical variations cannot be explained on chemical grounds because the mineral shows very little chemical variation but they can be explained on the basis of Al/Si ordering. The v{021} sectors (Pa setting) are composed of optically triclinic bands, and the k{110} sector consists of both triclinic bands and monoclinic homogeneous domains. An electrostatic charge of the Al/Si ordered structure is balanced along a two-dimensional atomic arrangement exposed on the side face of a growth step. If the Si tetrahedron is produced after the calcium ion, the Si ion will be replaced during growth by an Al ion due to the local effect of the calcium ions. When a side plane of growth steps of yugawaralite is not normal to the (010) glide plane, a symmetrical equivalence of two Si sites with respect to the Ca ion will be lost at the surface, and as a consequence ordering will occur and the symmetry of crystal will be reduced. The monoclinic, homogeneous sector might be produced on the very finely kinked surface. The space group of the triclinic sector will be P1, while that of the monoclinic sector will be Pc.