A new mineral, akaganéite, has been found in limonite deposits and has been shown to be identical with synthetic β-FeOOH. It contains no chlorine. The micro-morphology of β-FeOOH as it occurs as akaganéite and as it is produced by a solid-state transformation from FeCl2.4H2O , by the hydrolysis of dilute FeCl3 solutions, and by the hydrolysis of very concentrated FeCl3 a solutions, has been studied, chiefly by electron microscopy and diffraction. Some modes of colloidal association of the particles of β-FeOOH are described.

Florencite with ω 1·653, εd 1·661, G 3·457, a 6·971 ± 0·004 Å, c 16·42±0·13 Å, and rhombohedral unit-cell contents Sr0·42Ce0·52Ca0·14Al2·83(PO4)1·77(SO4)0·10 F0·41(OH)5·24(H2O)0·85 occurs in the Kangankunde carbonatite in Nyasaland, and goyazite with G 3·386, a 6·982±0·001 Å, c 16·54±0·02 Å, and rhombohedral unit-cell contents Ba0·05Sr0·50Ce0·41Ca0·08A2·78(PO4)1·62(SO4)0·19F0·30(OH)5·30(H2O)1·18 on the Wigu carbonatite in Tanganyika. Hydrothermal decomposition experiments in the Wigu material indicate stability below 535 ± 10 °C at pH2O 200 bars and 565 ± 10°C at pH2O 2500 bars ; both minerals exhibit endothermic peaks at 630°C in differential thermal analyses. The crystal chemistry of the goyazite series is discussed in the light of the two new analyses and of newly determined unit-cell dimensions for four other members of the goyazite series. Goyazite, florencite, and gorceixite appear to have crystallized during late-stage replacement processes or under supergene conditions in carbonatites.

The results are presented of some recent feldspar studies that relate the fundamental concepts of order-disorder series to petrological problems. New diagrams have been prepared with coordinates ‘optical properties-chemical composition-structural state’. From direct observations made on natural minerals some conclusions have been reached about the sequence in which the solid-state transformations of ordering, unmixing, and twinning occur in feldspars.

A study has been made of the geological distribution of different structural types of alkali feldspars in single intrusive bodies (Tertiary granite, Palaeozoic syenite, Pre-cambrian charnockite), in magmatic complexes, and in different complexes of the Ukrainian Shield and the Caucasus Geosynclinal Province.

Optical and other microproperties of owyheeite Pb5Ag2Sb6S15 are presented and details given of a new locality for this rare sulpho-salt. Apparent rotation of the plane of polarization (3·5°), microhardness (112 V.H.N.), and polarization effects are all very similar to those of the other feather ores, jamesonite and boulangerite. An intimate association with pyrargyrite is further noted.

The Archean rocks of the Barrier Ranges, New South Wales, show zones of progressive regional metamorphism of which the highest is characterized by orthopyroxene-bearing basic granulites. Within this zone, further increase in metamorphic grade results in a detectable change in distribution of ferrous iron and magnesium between coexisting orthopyroxene and clinopyroxene, the latter becoming relatively richer in iron. Mutual solid solution between the two pyroxene phases also appears to increase. The value of coexisting pyroxenes as indicators of metamorphic grade is thus established. There are some points of disagreement between the Broken Hill results and previously advanced theories of cation distribution in pyroxenes.

The trace-element assemblage of the cassiterite of the Turkaňk and Rejsy zones of the Kutná Hora mining district are typical of a hydrothermal sulphide-cassiterite formation. Polished section studies show replacement of cassiterite by pyrrhotine, with stannite as am intermediate zone.

Re-examination of hodgkinsonite by optical and X-ray methods has shown the desirability of adopting a setting different from that selected by Palache and Schaller and by Rentzeperis. In the new arrangement the b and c axes are interchanged and the original negative end of the b-axis becomes positive. A table of angles for the common forms is given, also X-ray powder data and a space group determination.