An illite separated from an Upper Old Red Sandstone sediment at Denholm Hill Quarry, Roxburghshire, when examined by optical, X-ray, and chemical methods, appeared to be closely similar to Fithian illite. Its composition was , where M+ for the Ca-saturated sample was [(H3O)0·58Ca0·10Na0·06K1·12]. The differential thermal curve showed two peaks: one at 550° C. and the other at 600° C. (i.e. somewhat intermediate between the Fithian and Ballater illites). The dehydration curve was also intermediate. Electron-microscope examination showed rather better crystallization than in Fithian illite. The possible reasons for variation of the illite peak temperature are discussed.

Metamorphosed dyke rocks in Witwatersrand gold mines carry pyrite crystals of unusual appearance. These crystals, particularly along the dyke margins, show curved and scratched surfaces that cut across crystal faces. The abrasion of the crystals is due to movement of dyke material under pressure. There is some suggestion of surface flow on the abraded surfaces. No deformation or granulation was obtained in laboratory experiments on pyrite crystals. Pressure shadows around the pyrite are described.

A simple photoelectric-cell attachment for use with an ordinary oremicroscope is described. Stabilization of the light source and accurate calibration of the photometer enable reflectivity values to be determined within an accuracy of 1% of the measured value. The choice of a universally acceptable standard is discussed. The photometer can be used with white light or with light of different wave-lengths. Bireflection, dispersion, and dispersion of the bireflection can readily be measured.

When one optic axis of a biaxial crystal has been located accurately by the usual orthoseopic or conoscopic methods, the second may be located by determining the extinction positions at normal incidence and applying the Biot-Fresnel construction. When use is made of the extinction directions associated with two or more wave normals inclined to the section, this method gives more reliable values of the optic axial angle than can be obtained by the doubling of the angle V over the pole of a bisectrix. If the optic axes have been located with sufficient accuracy by this procedure, then this also determines the orientation of the indicatrix.

The standard thermal treatments proposed by Lima-de-Faria have been applied to metamict euxenites, polymignites, yttrotantalites, samarskites, pyrochlores, and allanites. In the case of these metamict niobotantalates a facecentred cubic phase is formed at 700° C., and at 1000°C. a more characteristic phase appears combined with the cubic one. In the case of allanites only a slight formation or strengthening of the original structure of allanite appears at 700°C., and at 1000°C. a cubic phase is formed together with other phases.

A visual microphotometer depending on three polarizing screens is used to provide the primary scale for measuring the ratio of intensity between the incident and reflected beams for a prepared standard surface, which is intended for subsequent use in the ordinary procedure with the ore-microscope. A reversing mirror on the microscope stage gives reflection at quasi-normal incidence. Direct measurements on a surface of diamond confirm the validity of the Fresnel formula for a polished surface of this substance, and there is general agreement for a series of transparent bodies ranging up to 17 % reflectance. The standard is a glass-covered metallic surface with a reflectance near 50 %. For pyrite RD = 54·5 %.

Analytical data on a garnet-chlorite rock and the contained garnet with spectrographic determinations of the trace elements are presented, and the principles determining the distribution of these elements between the garnet and the chlorite are discussed.

Small crystals (2 mg.) of plagioclase and potassium felspar were irradiated for four weeks in an atomic pile. Subsequent analysis of the radiation showed that this is a possible method for the determination of the sodium and potassium content, and it should be possible to develop the method further in this direction. It has not proved a suitable method for the determination of calcium.

In the Torrington district of New South Wales the cassiterite occurs almost entirely in hydrothermal veins, with galena, blende, quartz, and chlorite; sometimes it replaces crinoid stems and gastropods. In the Madman vein, however, the cassiterite is associated with adularia, both minerals encrusting quartz. These observations suggest that the tin came in as alkali stannate solutions.

A small isolated outcrop in a large area of charnockites in the Mawson area, MacRobertson Land, Antarctica, consists of enstatite-sapphirine-cordierite rocks. Other highly magnesian outcrops occur in the district and these rocks may be completely recrystallized xenoliths. Analyses of the country rock, the two sapphirine-bearing rocks, and the sapphirine are given; the country rock is very rich in iron and has a high FeO : MgO ratio, while the sapphirine-bearing rocks are very low in iron and high in MgO, approximating to ternary mixtures of MgO, Al2O3, and SiO2.

This zeolite, hitherto recorded only from Chaux de Bergonne, France, has been found as zoned spherules with thomsonite (var. faroelite), on specimens from Aci Castello and Aci Trezza, Sicily, and Capo di Bove, Rome, from Weilberg, Rhineland, and from Klöch, Styria. Three chemical analyses confirm previous results; optical data suggest some variation in composition within a spherule. There is a striking resemblance between X-ray fibre photographs of gonnardite and of thomsonite, and between X-ray powder photographs of gonnardire and of natrolite. The Klöch occurrence, where the gonnardite is accompanied by phillipsite, is described in detail.

The space group and unit cell of natural syngenite have been redetermined. X-ray powder photographs of natural syngenite and synthetic CaSO4.K2SO4.H2O were found to be practically identical. Optical and d.t.a. data are also given.

A systematic and time-saving procedure for the correlation of optical or other physical properties with chemical composition is outlined, and is applicable even where the composition is complex and involves several variables. The procedure is applied to anthophyllite, for which the following partial regression equations are derived:

γ = 1·7249−0·0130Si+0·0140(Ti+Fe‴+Fe′+Mn)±0·0012,

β = 1·7275−0·0142Si+0·024(Ti+Fe‴)+0·0110(Fe″+Mn)±0·0015,

α = 1·6951−0·0117Si+0·040(Ti+Fe‴)+0·0133(Fe″+Mn)±0·0025,

b(Å.) = 16·44+0·28Si−0·13Mg+0·40(Ca+Na+K)±0·04.

The a and c cell-dimensions appear to be constant, within the experimental error of the available data.

The composition of carphosiderite has been given as

H2O.Fe3(SO4)2(OH)5H2O

and like the jarosites is characterized by a ferric iron to sulphate ratio of 3:2. It is significant not only that this formula was worked out on artificial material but also that none of the analyses so far made supports it. The present investigation shows that there is little or no evidence for the existence of a mineral with the above composition and that carphosiderites are in reality either jarosite or natrojarosite. It has long been thought that certain other minerals, namely borgströmite, utahite, cyprusite, pastréite, raimondite, apatelite, and planoferrite, were similar to, if not identical with, carphosiderite and six of these are listed with carphosiderite in Dana, Syst. Min., 7th edn. These minerals with the exception of planoferrite and the possible exception of apatelite are also jarosite or natrojarosite.