The author exhibited and described the small additions that need be made to an ordinary microscope, in order to make it available for the above-named purpose, and also gave a few illustrations of its application to particular minerals. So far, however, the instrument has been used only sufficiently to prove that the method gives excellent results. The author thinks it desirable to defer a complete decription of the construction and use of the instrument until he has been able to examine a sufficient number of minerals to publish a table of their indices of refraction for practical use. It may, however, be well to say that the addition to the microscope consists only in a small graduated scale attached to the body of the instrument, and vernier to read off to th of an inch. This enables us to measure the extent to which the focal length of the object glass is increased by looking through a more or less transparent miueral, and also its thickness in the part thus examined.

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.

While undergoing 'dry' homogenization at 980°C the 2̄01 X-ray reflections of sodic lowalbite- microcline microperthites show that phase compositions recapitulate (but in a reverse timesense) the unmixing history of ordered feldspars about a solvus with a critical composition near 26 mole per cent KAlSi3O8.

Rapid, accurate silica determinations have been made titrimetrically following decomposition by HClO4-HF in a ‘Teflon’ vessel, the volatilized silicon tetrafluoride being precipitated as K2SiF6 in a HF-KF-glycerol-alcohol mixture. After filtration and washing with alcohol the precipitate is dissolved in boiling water, then titrated with NaOH. This method has many advantages over conventional gravimetric or spectrophotometric procedures.

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.

The meteorite was an oriented polyhedron, which broke up into at least two parts after entry into the Earth's atmosphere. It has undergone some degree of terrestrial weathering. A cut surface of the meteorite shows light-grey interior with sporadic rusty-brown patches and a distinct brown alteration zone close to the fusion crust. Weathering has resulted in preferential replacement of NiFe by limonite, and veining of minerals by goethite.

Rewari is an equilibrated chondrite with rare ghosts of chondrules and at least one lithic fragment. Composition of olivine, as indicated by microprobe analysis is Fa23, which agrees well with bulk wet chemical analysis; that indicated by d130 is Fa18–20. From the outer surface inwards, four petrographic zones can be distinguished in the meteorite: a skin, about 0.01 mm thick, a troilite-poor zone slightly thicker than the skin, a troilite-rich ‘soaking zone’, about 0.5–0.6 mm thick, and a relatively coarse-grained interior. These are described in detail.

The interior of the meteorite is composed of relatively coarse-grained crystalline silicates with disseminated metallic minerals including plessitic and zoned inter-growths of kamacite and taenite. The matrix shows a high degree of integration with the chondrules. The coarse texture and zonation of taenite may be the result of protracted heat treatment responsible for recrystallization. The constituent grains show considerable shock effects such as fracturing, comminution, veins of shock-melted pseudotachylite, pressure twinning, and undulose extinction. Chemical composition (mean of two wet chemical analysis) of the meteorite is: metallic Fe 7.475, Ni 0.975, Co 0.045; as sulphide Fe 3.200, Ni 0.090, Co < 0.01; SiO2 38.060, TiO2 0.10, Al2O3 2.34, Fe2O3 0.175, Cr2O3 0.485, FeO 13.950, MnO 0.210, NiO trace, CaO 1.875, MgO 26.265, Na2O 0.89, K2O 0.115, P2O5 0.285, H2O− 0.295, H2O+ 0.81, CO2 trace, S (total) 1.890, C (total) 0.19 per cent. The chemistry, mineralogy, and texture show that the Rewari meteorite is an L6 chondrite. Compared to average L-group chondrite it has a higher content of MgO and lower of SiO2, a little lower oxidation state, and tends to be enriched in siderophilic elements.

A minor phase in iron-ore sinters has been synthesized and identified as a clinopyroxene with the approximate formula Ca1·0(Ca0·14Al0·60Si1·08)O6. This composition shows that it consists largely of the hypothetical Tschermak's molecule, M2+SiO6. The small size and sparse distribution of this phase in most iron-ore sinters has previously hindered analysis.