The accurate determination of α:[001] and 2V in members of the aegirine-augite series often presents difficulties owing to strong absorption and dispersion, especially as high angles of tilt on the universal stage are often involved. Both of these angles depend on the location of α, and this operation is the one most subject to error.

An alternative procedure is the determination of A:[001], the angle between an optic axis and [001]. This angle is very easily and accurately determined and varies systematically with composition. It can be derived from the values for α:[001] and 2V, while conversely values of α:[001] and 2V can be obtained from A:[001] by reference to standard curves.

Ancient metamorphic processes are recorded by the formation of metallic-Pb nanospheres in zircon, a product of internal Pb mobilisation and thermally driven concentration. Here, metallic-Pb nanospheres formed within an ore deposit are characterised for the first time using high-angle annular dark field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy element-distribution mapping. Exceptional examples from the migmatite-hosted Archean–Paleoproterozoic Challenger Au deposit (Central Gawler Craton, South Australia) support widespread metallic-Pb nanosphere formation in zircon from rocks experiencing granulite-facies metamorphism. We also report new trace-element associations found with metallic-Pb nanospheres and a new mode of occurrence, in which Sc ‘haloes’ form adjacent to metallic-Pb nanospheres within the crystalline zircon lattice. This differs to previously characterised examples of metallic-Pb nanospheres associated with amorphous Si-rich glasses and unidentified Al–Ti, or Fe-bearing phases. Multiple modes of metallic-Pb nanosphere occurrences and trace-element associations suggests multiple modes of formation, probably dependant on zircon composition and metamorphic conditions. Identification of metallic-Pb nanospheres in a growing range of geological settings further highlights the mobility of Pb in zircon and the importance of detailed, nanoscale mineral characterisation, in order to constrain accurate geochronological histories for rocks within high-temperature geological environments.

The mineral Leucite has for so long a period been considered as one of the most remarkable examples of limited distribution both in space and time, that the discovery in Australia of a rock largely composed of this mineral, by Mr. T. W. Edgeworth David, F.G.S., of the Geological Survey of New South Wales, is one that appears deserving of being at once placed upon record.

Leucite-crystals, under the head of "white garnet," or "white schorls," appear to have been known from a very early period ; and, indeed, the fine examples from Somma could scarcely fail to attract the attention of the older mineralogists. Subsequently it was found that the mineral occurs in other parts of Italy, and especially the neighbourhood of Rome, as well as at the Laacher See and the Kaiserstuhl.

During recent years a considerable industry has grown up at Paris in the synthetical manufacture of corundum for jewellery purposes by means of the process devised by Professor A. Verneuil. In place of the fragments of natural ruby used in previous attempts, ammoniumalum is the material employed. After careful preparation to free it from potash and other impurities, it is ground to a powder and placed in a sieve at the top of the oxygen tube of an inverted blowpipe. The sieve is tapped by a hammer at regular intervals, and uniformity is in this simple way produced in the amount of powder that falls; the necessary adjustment is effected by varying the height through which the hammer falls. To minimize the cost of production, a few alterations have been made in the original apparatus.

The instrumentation and procedure is described for the extraction of very small and pure samples from polished mounts and thin sections of minerals, for X-ray analysis and other micro-analytical techniques. It uses a stand-mounted, tunable ultrasonic probe (400 W/15–50 kHz) inclined at 45°C to a microscope stage. The tip of the probe, usually a steel needle, is located on the desired mineral and an appropriate ultrasonic frequency is selected. Very fine powders are produced from grains as small as 0.01–0.005 mm. A distinct advantage of this technique is that, as different minerals powder at different rates and different frequencies, it is possible to separate a single mineral from an intergrowth of two or more minerals.

Two new finds of stony meteorites north-west of Kalgoorlie are described, and the masses covered by brief petrographic descriptions.

Dendoraite-(NH4), (NH4)2NaAl(C2O4)(PO3OH)2(H2O)2, is a new mineral species from the Rowley mine, Maricopa County, Arizona, USA. It occurs in an unusual bat-guano-related, post-mining assemblage of phases that include a variety of vanadates, phosphates, oxalates and chlorides, some containing NH4+. Other secondary minerals found in association with dendoraite-(NH4) are antipinite, fluorite, mimetite, mottramite, relianceite-(K), rowleyite, salammoniac, struvite, vanadinite, willemite, wulfenite and at least one other new mineral. Crystals of dendoraite-(NH4) are colourless blades up to ~0.1 mm in length. The streak is white and lustre is vitreous, Mohs hardness is 2½, tenacity is brittle and fracture is splintery. The calculated density is 2.122 g⋅cm–3. Dendoraite-(NH4) is optically biaxial (–) with α = 1.490(5), β = 1.540(5) and γ = 1.541(5) (white light); 2Vcalc = 15.7°; and orientation X = b. Electron microprobe analysis gave the empirical formula [(NH4)1.48K0.52]Σ2.00Na0.96(Al0.96Fe3+0.03)Σ0.99(C2O4)[PO2.97(OH)1.03]2(H2O)2, with the C, N and H contents constrained by the crystal structure. Dendoraite-(NH4) is monoclinic, P21/n, with a = 10.695(6), b = 6.285(4), c = 19.227(12) Å, β = 90.933(10)°, V = 1292(2) Å3, and Z = 4. The structural unit in the crystal structure of dendoraite-(NH4) (R1 = 0.0467 for 1322 Io > 2σI reflections) is a double-strand chain of corner-sharing AlO6 octahedra and PO3OH tetrahedra decorated by additional PO3OH tetrahedra and C2O4 groups. Topologically, this is the same chain found in the structure of thebaite-(NH4). The decorated chains connect to one another through links to NaO7(H2O) polyhedra to form a [Na(H2O)Al(C2O4)(PO3OH)2]2– sheet, which connect to one another through bonds to (NH4)/K and through hydrogen bonds.

Favourability of uranium mineralization in six tertiary granitic plutons of the Alaska Range in the Talkeetna and Mt McKinley quadrangles was studied. The uranium concentrations of drainage sediment samples, which were collected and analysed by the Los Alamos Scientific Laboratory for the National Uranium Resources Evaluation, were statistically evaluated and compared to those of the surrounding area using factor and cluster analyses. The results of this study suggest that five of the six plutons under consideration are likely to contain uranium mineralization. These plutons are probably a potential source rock for uranium in the region.