Scarbroite, a fine-grained but compact deposit obtained from fissures in the sandstone on the north Yorkshire coast, is shown by chemical analysis to have an idealized formula Al2(CO3)3·12Al(OH)3. X-ray and electron diffraction data indicate a triclinic cell with a 9·94 Å., b 14·88 Å., c 26·47 Å., α 98·7°, β 96·5°, and γ 89·0°. A layer structure consisting of gibbsite-type sheets of Al(OH)3 and sheets of Al2(CO3)3 is proposed. The structure is stable from room temperature to about 125° C.

Electron micrographs of scarbroite show thin platy crystals of about 1 μ size, having rhombic outlines with angles 66° ± 1° and 113° ± 1°. Single-crystal electron-diffraction patterns show rectangular net patterns, with d100 = 9·90 Å., d010 = 14·67 Å., γ* = 90° ± 0·05°. Strong hk0 reflections show a pseudohexagonal arrangement, but true symmetry is probably orthorhombic or monoclinic. Faces outlining rhombic forms are of type {11l}, .

A number of representative examples of the Lewisian acid pegmatites of South Harris are described, and the presence of the following minerals has been established: quartz, albite, microcline, biotite, muscovite, magnetite, beryl, spessartine, gahnite, eolumbite, monazite, zircon, pyrite, epidote, tourmaline, apatite, thorite, uraninite, thorogummite, uranophane, kasolite, betafite (?), and allanite. Spectrographic, optical, and X-ray powder data are given for some of these minerals, together with chemical analyses of magnetite, biotite, columbite, gahnite, and spessartine. It is believed that gahnite, nranophane, and the pyrochlore mineral (probably betafite) are recorded for the first time from Britain.

The single crystal X-ray methods for the study of exsolution phenomena in pyroxenes previously described by the authors have been applied to the pyroxenes of the Skaergaard intrusion. The results for about fifty pyroxene crystals, selected from various levels between the chilled margin and a height of 2600 metres in the layered series, are presented and are correlated with previous optical descriptions. Whilst the correlation between the results of the optical and X-ray examinations is in general satisfactory, the present investigation shows that the X-ray techniques can in some cases extend our knowledge of the Skaergaard pyroxenes.

A nordmarkite from the Ben Loyal syenite complex has been analysed, in which a powdery yellow mineral occurs in miarolitic cavities. The mineral may be a new hydrated species with a monazite structure and a chemical composition essentially that of monazite but with silicon partly replacing phosphorus and with magnesium, calcium, and iron partly replacing the rare earths.

Attention is drawn to anomalies in the nomenclature of the niobatetantalates, and the fergusonite series as used by Dana is renamed the fergusonite-formanite series. Chemical variations in this series are discussed with particular reference to H2O, Ca, Ti, Yt, individual lanthanons, Th, and U. Members of the series usually show heavy lanthanons exceeding light lanthanons but one specimen shows high Gd+Tb+Dy.

Two compounds, one an apatite and the other a perovskite, have been synthesized by sintering mixtures containing CaO and Cr2O3, and CaO, Cr2O3, and Fe2O3 respectively. The apatite formed by partial oxidation of the Cr2O3 and subsequent pick-up of moisture from the atmosphere, to give Ca5(CrO4)3OH. The perov-skite formed as a non-stoicheiometric compound Ca4(Fe,Cr)4O11 by partial oxidation of the Cr2O3 during firing. Lattice parameters and interplanar spacings are given for the two structures.

Sepiolite found as a minor constituent of dolomitie marble bordering tremolite rock from the southern contact zone of the Quérigut granite is briefly described and optical data are presented. A possible paragenesis, following on break-down of the tremolite under the action of carbon dioxide, is suggested.

Thaumasite has been found in a dolerite sill at Ballyalton, Co. Down, Northern Ireland. Indexed powder data for the mineral are given.