Specimens of trachyte obtained on a recent visit to the Kaiserstuhl are compared with similar potassium-rich rocks from carbonatite complexes in Africa. Two new chemical analyses are given, in which the values for alkalis (Na2O 1·21, K2O 12·63; Na2O 0·92, K2O 12·18 %) are of interest.

The distribution of trace elements is studied in different acid and basic rocks, adjacent to the copper lodes in the Mosaboni mines, Singhbhum, and adjoining the thrust zone, as well as of areas far away from the mineralized zones. Specific differences in composition and trace constituents in these rocks especially as regards S, Cu, Ni, and Co, suggest that the relationship of the Singhbhum granite with the soda granite is most unlikely, and that there is a connection between the soda granite and the sulphide ore-fluid ; a genetic relationship of sulphide mineralization with the epidiorite is doubtful. The possibility of the existence of a common source for the Chotanagpur granite and the Singhbhum granite is inferred.

The chemical formula of fiedlerite, a rare hydrated lead halide, has been revised. The mineral is now known to contain also fluorine, and the new, correct formula is Pb3Cl4F(OH)·H2O. X-ray diffraction studies on fiedlerite from Laurion, Greece (the type locality), and from Baratti, Italy (the second known occurrence), revealed its Order-Disorder (OD) character. All structures within this OD family can be built up by layers of the same kind. The two polytypes with Maximum Degree of Order (MDO) display triclinic and monoclinic symmetry, with one and two OD layers, respectively, in the unit cell. On these grounds the nomenclature of fiedlerite has been revised, and the mineral is designated together with the polytype suffix (i.e. fiedlerite-1A, fiedlerite-2M). The crystal structures of the two MDO polytypes of fiedlerite have been solved and refined: fiedlerite-1A: P, a = 8.574(3) Å, b = 8.045(4), c = 7.276(2), α = 89.96(4)° β = 102.05(4), γ = 103.45(4), R = 0.092; fiedlerite-2M: P21/a, a = 16.681(4) Å, b = 8.043(3), c = 7.281(2), β = 102.56(4)°, R = 0.061. In both structures Pb is eight-coordinated by different ligands [CI−, F−, (OH)−, H2O] that define bicapped trigonal prisms.

Sepiolite has been identified in the Keuper Marl at a Midlands locality by X-ray diffraction data, electron microscopy, differential thermal analysis, and chemical analysis. It has been calculated that a sample representing 30 ft. thickness of clay may contain as much as 39 % sepiolite. Apart from sepiolite, the Keuper Marl in the area examined consists mainly of mica, quartz, calcite, and ferric oxide.

Some years ago the author gave a short description of a quartz-bearing syenite and its xenoliths occurring on the eastern side of Barnavave. The locality was revisited recently and more material wascollected, while another outcrop of syenite was discovered farther tothe north at locality 5.

The new material collected at the original locality is not very differentfrom that previously described. The syenite occurs as veins in lime-stone and, whereas all the previously described material was quartz-bearing, some of the syenite in very narrow veins is virtually free fromquartz. Again, certain specimens carry a fair amount of late-crystallizing wollastonite which may be replaced to a varying degree by pecto-lite.

The crystal structure of carminite, PbFe2(AsO4)2(OH)2 has been refined. The mineral is orthorhombic, Cccm with a = 16.591(2), b = 7.580(1), c = 12.285(1) Å, Z = 8; the structure has been refined to a conventional R = 3.3% using 913 observed reflections [I>2σ(I)]. The structure contains stepped chains of edge-sharing pairs of Fe(O,OH)6 octahedra; these chains are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination. The hydrogen bonding network in the structure has been modelled using bond valence calculations.

Phase equilibria involving solids, liquids, and vapours on the join Ca(OH)2-CaF2-Ca3(PO4)2-H2O were determined at 1000 bars. The temperatures and liquid compositions (weight %) of the isobaric invariant reactions encountered were: portlandite+fluorite → liquid, 687° C, 70 % Ca(OH)2 30 % CaF2; portlandite+fluorite+vapour → liquid, 675° C, 69% Ca(OH)2 26 % CaF2 5 % H2O; portlandite+fluorite+apatite → liquid, 675°C 73 % Ca(OH)2 24 % CaF2 3 % Ca3(PO4)2; portlandite+fluorite+apatite+vapour → liquid, 665° C, 70 % Ca(OH)2 22 % CaF2 3 % Ca3(PO4)2, 5 % H2O. The temperatures of these reactions were determined from over 400 experimental runs at selected pressures from 250 to 4000 bars. The composition of the apatite involved in the last two reactions was 60 % hydroxyapatite 40 % fluorapatite and in subsolidus regions in the presence of water, fluorapatite did not crystallize but fluorhydroxyapatite solid solutions coexisted with vapours containing up to 2·5 % hydrogen fuoride. These observations suggest that hydroxyapatite is more stable than fluorapatite at elevated temperatures and pressures and would be the composition expected to crystallize under igneous and metamorphic conditions.

Sea-water from Deception Island was found to contain 0·55–1·48 mg Mn 1−1 and 10·2-64·3 mg Si 1−1. Reaction of Deception Island basalt and sea-water at 190 °C and 500 bars simulated the measured water composition but leaching experiments suggest that much of the Mn etc. may derive from local volcanic ash. Mn and Mg in thermal waters at Reykjanes have concentrations compatible with equilibrium with components of montmorillonite present as an alteration mineral of average composition . However, Fe is controlled by equilibrium with sulphides. Flux calculations based on these and other data place upper limits on hydrothermal Mn input to the oceans of 5–36×1011 g yr−1 and Mn accumulation in metalliferous sediments of 2–9×1011 g yr−1.

The second occurrence of the asbestiform silicate carlosturanite is reported. The mineral occurs in Taberg, Sweden, and it was previously reported as ‘picrolite’, that is fibrous antigorite. Carlosturanite from Taberg is non-pleochroic, green in colour and has positive optical elongation. The unit cell parameters are a = 36.55, b = 9.31, c = 7.27Å, β = 101.05°. Based on the determined formula, (Mg20.47Fe0.59Mn0.06Cr0.01Ti0.01) (Si11.68Al0.28)O27.81(OH)34.19H2O carlosturanite can be expected to crystallize within the pure MgO-SiO2-H2O system as a low-grade metamorphic mineral.

Because there are close similarities in structure and properties of carlosturanite and the picrolite variety of antigorite, their distinction requires careful attention to X-ray and electron diffraction patterns and chemical compositions. The present identification of the Taberg specimen as carlosturanite puts a lower limit of 33.7 Å to the known range of a parameters of antigorite.

The crystal structure of tlapallite has been determined using single-crystal X-ray diffraction and supported by electron probe micro-analysis, powder diffraction and Raman spectroscopy. Tlapallite is trigonal, space group P321, with a = 9.1219(17) Å, c = 11.9320(9) Å and V = 859.8(3) Å3, and was refined to R1 = 0.0296 for 786 reflections with I > 2σ(I). This study resulted from the discovery of well-crystallised tlapallite at the Wildcat prospect, Utah, USA. The chemical formula of tlapallite has been revised to (Ca,Pb)3CaCu6[Te4+3Te6+O12]2(Te4+O3)2(SO4)2·3H2O, or more simply (Ca,Pb)3CaCu6Te4+8Te6+2O30(SO4)2·3H2O, from H6(Ca,Pb)2(Cu,Zn)3(TeO3)4(TeO6)(SO4). The tlapallite structure consists of layers containing distorted Cu2+O6 octahedra, Te6+O6 octahedra and Te4+O4 disphenoids (which together form the new mixed-valence phyllotellurate anion [Te4+3Te6+O12]12−), Te4+O3 trigonal pyramids and CaO8 polyhedra. SO4 tetrahedra, Ca(H2O)3O6 polyhedra and H2O groups fill the space between the layers. Tlapallite is only the second naturally occurring compound containing tellurium in both the 4+ and 6+ oxidation states with a known crystal structure, the other being carlfriesite, CaTe4+2Te6+O8. Carlfriesite is the predominant secondary tellurium mineral at the Wildcat prospect. We also present an updated structure for carlfriesite, which has been refined to R1 = 0.0230 for 874 reflections with I > 2σ(I). This updated structural refinement improves upon the one reported previously by refining all atoms anisotropically and presenting models of bond valence and Te4+ secondary bonding.

Urea, a new mineral identical with the artificial compound, occurs as crystals associated with phosphammite, ammonian aphthitalite, and weddellite in guano from Toppin Hill, 123° 56′ E., 28° 42′ S., Western Australia. The urea occurs as elongated tetragonal pyramids, space group , a 5·646, c 4·701 Å, X-ray powder data are given. Optical properties: ω 1·484, ε 1·603. Chemical analysis gave urea, CO(NH2)2 96·0, H2O− 0·46, Na 0.13, K 0·35, Ca 0·07, Mg 0·03, S 0·11, P 0·24, NH3 < 1·0 %, remainder probably mainly H2O+; urea 96 %, impurities 4 %. Type material is preserved in the collection of the Government Chemical Laboratories, Perth, Western Australia.

Measurements of fine-grained dolerites by optical automatic image analysis are used to illustrate the effects of magnification and resolution on the values obtained for grain ‘size’, grain boundary length, surface area per unit volume, and other parameters. Within the measured range of optical magnifications (× 26 to × 3571) and resolutions (1.20 × 10−3 cm to 8.50 × 10−6 cm), it is found that the values of all grain parameters estimated by chord size analysis vary with magnification. These results are interpreted in terms of the concepts of ‘fractal dimensions’ introduced by Mandelbrot (1967, 1977). For some comparative purposes the fractal relationships may be of little significance as relative changes of size, surface area, and other parameters can be expressed adequately at given magnification(s). But for many studies, for instance in kinetics of grain growth, the actual diameter or surface area per unit volume is an important dimension. The consequences are disconcerting and suggest that it may be difficult in some instances to specify the ‘true’ measurements of various characteristics of fine-grained aggregates.

An unusual monazite deposit of metasomatic origin is described. The monazite occurs as randomly oriented crystals in a dolomitic marble. The chemical composition and optical data of the monazite are given.

Deerite in two meta-ironstones from Papua New Guinea coexists with quartz-albite-riebeckite-dannemorite-magnetite-spessartine-stilpnomelane-apatite-Ca/Mn carbonates and quartz-albite-crossite-ilmenite-spessartine-stilpnomelane-apatite respectively. Geochemical comparisons in the system FeO-MnO-MgO suggest that the P.N.G. deerites most closely resemble Franciscan types. However, the metamorphic assemblages more closely resemble Alpine types indicating metamorphism close to the lower P-T limit of deerite stability. Consistent differences in whole-rock and internal oxidation ratios between the two specimens suggest that fo2 may be important in determining deerite chemistry. A redox equation is suggested linking changes in deerite internal oxidation ratio with variable OH content.

Descriptions, with chemicaland mineralogical data, are given of zoned wollastonite-grossular-clinozoisite skarns found at the contact of limestone and granite at Puyvalador, near Quérigut, France. It is shown that the silica and alumina necessary for the formation of the skarn were supplied by the adjacent granite, which in return received lime from the marble replaced by the skarn zones. The modified facies of the granite in contact with the skarn is also described; it shows evidence of migration of silica towards the contact and of accumulation of lime derived from the neighbouring marble.

Similar, but not identical, changes are found at other localities along the Quérigut granite contact with limestone. The features of the Puyvalador granite-limestone contacts are compared and contrasted with those described from some other regions. The contact rocks dealt with here are characterized by the presence of abundant clinozoisite, indicative of relatively low temperatures and abundance of water at the contact in the later stages of evolution of the granite.

A remarkable series of wollastonite-garnet-idocrase veins occurs in the limestone quarries of Lough Anure in the Thorr area of Donegal. This locality lies on the extreme south of the one-inch Geological Survey of Ireland Sheet no. 9, and on the six-inch O.S. Sheet no. 41. S.E. In this area large isolated relics of Dalradian sediments are surrounded by a quartz-diorite which is highly modified at the contacts. This complex is intruded by an alkali-granite. The relict masses may be roof pendants or enclosures, and they are certainly structurally related to one another. It is the purpose of the present paper to describe the mineralization of one particular set of veins in a limestone forming part of one of the masses and exposed in two quarries about 300 yards SW. of the Lough Anure Technical School.

X-ray laboratory diffraction contrast tomography (LabDCT) produces three-dimensional (3D) maps of crystallographic orientation. The non-destructive nature of the technique affords the key benefit of full 3D context of these, and other, in situ measurements. This study is the first to apply the technique to any material other than a metal or silicon. We report the first 3D measurements of the crystallographic orientation of olivine, which also makes this study the first to apply LabDCT to (1) a non-metallic, non-cubic system and (2) geological material. First, we scanned fragments of olivine set in resin alongside glass microbeads using LabDCT and absorption contrast tomography (ACT). Then we reconstructed these data assuming an orthorhombic crystal system. We show that: (1) the regions within the sample that index well according to the orthorhombic system correspond to olivine fragments in the ACT image; (2) crystalline regions not corresponding to olivine are not indexed assuming the same lattice parameters; and (3) the diffraction data discriminates crystalline from non-crystalline materials as expected. Finally, we demonstrate that the method resolves sub-degree orientation differences between distinct regions within individual olivine fragments. We conclude that DCT can be applied to the study of rocks and other crystalline materials, and offers advantages over conventional techniques. We also note that LabDCT may offer a solution to the crystallographic measurement of substances that would otherwise be difficult to measure due to challenges in obtaining a perfect sample polish. Future developments to accommodate larger experimental volumes and additional crystallographic systems within a sample promises to expand the applicability and impact of DCT.