Stokesite was found in a lithium-bearing pegmatite at Ctidružice near Moravské Budějovice in Western Moravia (Czechoslovakia) in a close association with cryptocrystalline cassiterite. The type of its occurrence is described and its X-ray powder diffraction data given. This represents only the second occurrence of this very rare hydrous silicate of tin and calcium.

A new mineral with the approximate composition of Fe2MgTi3O10 and isostructural with pseudobrookite Fe4Ti2O10 has been observed in an olivine-augite-alkali-feldspar rock of the Karroo succession from the Mateke Hills area in south-eastern Southern Rhodesia. Chemical analysis and indexed X-ray powder data (α 9·77, b 9·95, c 3·73 Å.) of the mineral are given, and the name kennedyite is proposed. The name karrooite is proposed for the artificial product MgTi2O5.

The crystal structure of the clay mineral dickite (Al2Si2H4O9) has been refined to a greater accuracy than that reported in an earlier analysis. Improved lattiçe parameters are: a 5·15±0·001, b 8·940±0·001, c 14·424 ± 0·002Å., β 96° 44′± 1′. The dickite structure shows several significant distortions from the geometry of the idealized kaolin layer, including deformation and rotation of the silica tetra-hedra. The most striking features of the octahedral layer are the extremely short shared edges of 2·37 Å. Although the analysis was not sufficiently accurate to position the hydrogen atoms with certainty, a model consistent with the infrared absorption spectra is proposed. The stacking sequences of kaolin-layer minerals have been considered with reference to the structural features observed in dickite. There are thirty-six ways of superposing two kaolin layers commensurate with the OH-O bonds found in kaolinite, dickite, and nacrite. The twelve sequences showing the least amount of cation-cation superposition between consecutive kaolin layers can be used to construct two one-layer cells, kaolinite and its mirror image, and twelve two-layer cells, including dickite and nacrite. The distortions of the kaolin layer introduce secondary variations in the interlayer bonding that suggest that dickite and nacrite are the most stable of the kaolin layer structures, since they possess the shortest oxygen-hydroxyl contacts.

The top 2 inches of the Lower Magnesian Limestone is feebly but persistently mineralized along its outcrop from Nottingham to Doncaster, predominantly with galena and a little cerussite, frequently with uraniferous asphaltite containing 0·2 to 1% U3O8. Wulfenite, both platy and pyramidal in habit, occurs at Bulwell and Kirkby in Ashfield. The mode of formation and the age of these minerals are discussed.

The following ages determined by the complete lead method have been accepted for minerals from a number of localities: uraninite, Nkana, Northern Rhodesia, 522±15 m.y. ; brannerite, Kansanshi, Northern Rhodesia, 503±15 m.y. ; uraninite, Shinkolobwe, Katanga, 642±20 m.y. ; davidite, Mavuzi, Mozambique, 578±15 m.y.; monazite, Monkey Bay, Nyasaland, 597±25 m.y.; samarskite, north-west Kenya, 635±25 m.y. The significance of the results is briefly considered.

The mineral assemblages developed in a variety of high-grade metamorphic rocks from southern Nyasaland are compared with standard metamorphic facies mineral assemblages proposed by some authors.

A new occurrence of holmquistite is described. The mineral is found in amphibolite at the contact of a lithium pegmatite. Chemical analyses and optical data of the holmquistite and an associated hornblende are given.