It has long been realized that grinding increases the cation-exchange capacity of minerals and that it damages their crystal structures. However, while a considerable amount of data has been accumulated with regard to the effect upon various minerals, and clay minerals in particular, very little is known about how micas behave and such results as are available are somewhat inconsistent (1, 2, 3). In view of this and of a fortuitous observation that short-period grindingin an agate mortar affected the nature of muscovite considerably, a more detailed study of this subject has been undertaken.

This note describes a hydrous gedrite from Glen Urquhart for which the presence of an appreciable excess of oxygen atoms over the normal 96 per unit cell has been established. This is associated with an approximately equal deficiency of cations. The type of isomorphous replacement here discussed is hitherto unrecorded in the amphibole group.

The ejected blocks found in the 'peperino' of the Alban Hills have long attracted the attention of mineralogists on account of their variety in content of well-crystallized minerals. It may be recalled that this Roman region provides the earliest and finest examples of the white octahedral haiiyne, at first referred to a separate species (berzeline), and that this mineral with leueite, yellow garnet, wollastonite, green clino-pyroxene, and melilite form characteristic assemblages in the tufts from Albano, Frascati, and other places.

The fluorites of the Transvaal occur in different rock-types, viz in the dolomite of the Transvaal System, in acidic rocks (red granite and granophyre of the Bushveld igneous complex and Rooiberg felsites), and in alkalic rocks. The purpose of this study was to determine:

1. (1) What minor elements are present in selected fluorites.

2. (2) What the effect of these elements is on the respective cube-edges.

3. (3) Whether these elements have any geological significance.

Fluorite displays a wide range of colour; both colourless and distinctly coloured specimens were examined. Differently coloured varieties could in some instances be taken from the same sample. The choice of coloured varieties in the different rock-types was nevertheless limited. Only light-coloured fluorites occur in the dolomite, whereas the alkalic rocks yielded only very dark purple specimens.

Numerous investigations of the effect of heat on minerals of the kaolinite group have established that these minerals are characterized by two major thermal reactions below 1000° C. An intense and abrupt endothermal reaction between 500 and 600° C. has been attributed to the loss of chemically combined water from the kaolinite structure. At about 980° C. these minerals experience an exothermal effect. The intensity and rapidity of this reaction indicate a crystallization process. Certain investigators have ascribed this reaction to the crystallization of gamma alumina (Insley and Ewell, 1935). Comeforo, Fischer, and Bradley (1948), on the other hand, have concluded that it represents crystallization into mullite nuclei of articulated units derived from the original material.

The majority of amphiboles conform to the general structural formula X2-3Y5Z8O22(OH,F,Cl)2, where X = Na, K, Ca, Y - Mg, Fe″, Mn, A1, Fe‴, Ti, and Z = Si, A1 or Ti. Two X ions occupy the positions filled by Ca in the ideal tremolite structure; the additional X ions are assumed to occur in the 'A' sites which are vacant in tremolite.

For the amphiboles, therefore, the method most commonly adopted for deriving a formula from a chemical analysis is to assume that a total of 24 anions is present in the formula unit.

The most striking rock now described occurs in the Northern Province of Tanganyika Territory, just west of the Great North road, and south of the track from Longido to Engare Naibor. A small group of specimens was collected by Mr. A. G. Clough of Industrial Minerals Ltd., and presented to the British Musemn (Natural History) in 1952 (B.M. 1952,133). The outcrops occur in the highly metamorphosed Basement Complex which forms small hills (The Matabatu Mountains) descending, at their margin, by step-faulting to a peneplaned surface cut out of much younger, unconformable volcanics; the faulting in the marginal area of the basement rocks forms the eastern side of the Rift Valley. The basement rock adjacent to the zoisite-amphibolite is usually anamphibolite with conspicuous large, brown-red garnets. The occurrence of this garnet-amphibolite is usually an indication of the proximity of the zoisite-amphibolite.

Shortly after the discovery of the mineral kalsilite, the pure potash analogue to nepheline, as a natural mineral occurring in some volcanic ]avas of SW. Uganda by Bannister and Hey, Professor Arthur Holmes suggested that the ncpheline-looking ruineral occurring in a very potash-rich lava at San Venanzo, Umbria, Italy, also might be kalsilitc. His suggestion was based on the high potash : soda ratio of the bulk rock and on the optical properties of the mineral. No X-ray evidence or chemical analysis on the supposed kalsilite has been presented so far.

The basic technique for preparing micro-thin rock-sections has altered little since this method of studying rocks was first accepted. Abrasive powders were, and still are, used either on glass or metal plates, the grinding being done entirely by hand. At the present time carborundum is almost universally used as the abrasive. The technique has been speeded up somewhat by the use of horizontal metal laps, and in more recent years the introduction of high-speed diamond-cutting and lapping apparatus has considerably reduced the time involved in making a thin rock-section. But even with this apparatus the process is still long and laborious, and, even more important, the operator must have considerable skill and experience in keeping the specimen whole and of uniform thickness throughout the entire operation.

Thirty-Four specimens of australites were collected by Miss N. Jones and her brother Mr. Jones, during forty years while working on their property of 2000 acres, on the north bank of the Glenelg river. This is situated 3½ miles due east of Harrow (37° 8' S., 141° 33' E.) in the western district of Victoria, 236 miles north of west of Melbourne. The collection was kindly submitted for examination through Mr. E. D. Gill of the National Museum, Melbourne.

Occurrence and relationships. Altered and garnetized gabbros occur in association with serpentinite occupying the lower south-eastern slope of Byne Hill, one mile to the south of Girvan. The rocks crop out above Balaclava Wood near the footpath from Bynehill Bridge to Craiglea. Although the precise form of the altered gabbros is not very well revealed, they appear to be dikes intrusive into the surrounding serpentinized harzburgite. Contacts with the serpentinite are exposed in two places but are evidently lines of later movement. The relationships of these altered gabbros to the main gabbro mass of Byne Hill are obscure. They are, however, probably contemporaneous, since sporadic garnetization of the main gabbro occurs along its contact with serpentinite farther to the south-west.

The minerals to be described were found by Dr. Duncan M. Morison, of Edinburgh, and the writer in a small quarry having a national grid reference of 29/076184, which is at present being excavated for road surfacing material. The quarry is situated on the east side of the coast road between Lochinver and Ullapool at a point ¼ mile south-west of the southern margin of Loch an Arbhair (called Loch a' Choin on early editions of the Ordnance Survey sheet 101) and ¾ mile south-west of the bridge carrying the Lochinver-Ullapool road over the river Kirkaig, the course of which here marks the boundary between the counties of Sutherland and Ross.

An easily constructed apparatus, giving illumination by light of any chosen colour, and of adequate purity in a narrow spectral region, has been made and found satisfactory in the determination of the optical properties of crystals.

Light of high intensity is focused on an adjustable slit, rendered approximately parallel by means of a lens, and passed through two hollow prisms containing alpha-monochloronaphthalene. In the widely divergent spectral beams the microscope moves along a calibrated arc and any desired wave-band of reasonable purity may be selected. The apparatus is illustrated in the accompanying diagram (fig. 1) and photograph (fig. 2).

A small carbon arc (A) using direct or alternating current gives adequate intensity, allowing for a narrow setting of the slit, with corresponding purity of the monochromatic beam.

In a recent paper (hereafter referred to as GD) Goodyear and Dufiln (1954) described X-ray powder data for a number of synthetic and chemically analysed plagioclases of composition An0Abl00-Anl00Ab0. Important aspects of this work were a correlation of the X-ray patterns with chemical composition, and a distinction between the pattern of a naturally occurring material of low-temperature origin and that of a synthetic of similar composition. The investigation showed quite clearly that the unit-cell dimensions of a synthetic plagioelase depend but little on composition from An0Abl00 to An70Ab30, whilst they differ from those of the low-temperature modification greatly for albite, to a lessening degree as the composition approaches An70Ab30, and practically not at all in the range An70Ab30-Anl00Ab0.

The Beaver Bay diabase forms an irregular sill-like intrusion about 3000 feet in thickness exposed over a distance of approximately six miles from Split Rock to Beaver Bay on the north shore of Lake Superior, Minnesota. It is intrusive into the Keeweenaw volcanic series above the Duluth gabbro to which it is almost certainly related. It is the largest of many such sills in this region and includes several petrographic facies grading from troctolite, through olivine-gabbro, normal gabbro, and ferrogabbro to red granite.

Some years ago a few small grains of an unknown mineral were separated by F. H. Stewart from well cuttings from the Permian lower evaporite bed of the Eskdale no. 2 borehole, sunk by the D'Arcy Exploration Company near Aislaby, north Yorkshire. The mineral (not then identified) was mentioned in an account of the mineralogy of this evaporite bed (Stewart, 1949, p. 626). Flame tests suggested that boron and strontium were present, and this was confirmed by Dr. R. L. Mitchell of the Macaulay Institute for Soil Research in Aberdeen, who, by spectrographic work, found that these were the main constituents, and that very much smaller quantities of Ca, Mg, Ba, Na, and K were present.

A Granite (G-1) from Westerley, Rhode Island, and a diabase (W-1) from Centerville, Virginia, were recently analysed by some 34 analysts in different countries for the purpose of obtaining thoroughly reliable rock standards for spectrochemical analysis. Most determinations were made by so-called classical methods of chemical analysis. The results of the investigation have been discussed by Fairbairn and others. Fairbairn examined the results statistically and, using the relative deviation (standard deviation expressed as a percentage) as a measure of precision, concluded that precision deteriorated with a decrease in the concentration of a constituent. In the present paper this general observation will be demonstrated quantitatively by means of a graphical presentation, thus providing the petrologist with a guide for rapidly assessing and comparing the precision of classical methods of chemical analysis over considerable concentration ranges.

Specimens of the minerals beryl and löllingite were found by me among material collected in the summer of 1950 and the spring of 1951 for work on the distribution of trace elements in the New Consols mine, Stoke Climsland, Cornwall. Unfortunately, I was unable to collect further material, and in the case of the 1ö11ingite its presence on a specimen was recognized only after the mine had been abandoned and become flooded. This locality for the two minerals seems worthy of record in view of the small number of reported occurrences in Cornwall.

The beryl was found in specimens from a pegmatite vein, approximately 2 feet thick and dipping steeply southwards towards the main granite boss of Kit Hill, which was intersected 222 yards from the engine shaft by a south cross-cut at the 52-fathom level.

During a recent investigation of the hydrothermal mineralization associated with the Shap granite, nacrite was found in a quartz vein in the Shap Blue quarry. This quarry has been opened for roadstone in the metamorphosed Borrowdale lavas, 700 yards north of the granite contact on the west side of the Penrith-Kendal road, three miles south of Shap village. Further examination showed that nacrite often coats shear joints in fault breccias and shatter belts in the metamorphosed andesites. It is associated with chlorite, haematite, pyrite, and traces of erythrite, and often with later quartz, calcite, and baryte veins.

Nacrite from this locality occurs as microcrystalline aggregates on joint faces, usually only in thin layers but layers up to 5 mm. thick have been found.

Lindgrenite, a basic copper molybdate Cu3(MoO4)2(OH)2, was first described in 1935 by Palache from the oxidized zone of the great copper deposit at Chuquicamata, province of Antofagasta, Chile. A second occurrence has been recently described from the Helena mine in the Seven Devils mining district, Adams Co., Idaho, the first recorded in the U.S.A. In this paper we are able to record a third occurrence; this time in Cumberland, adding another species to the list of British minerals.