The ordinary quartz wedge is adapted for use by the colour blind by the superposition of a two-colour isotropic auxiliary plate. A birefringent plate of suitable retardation may also be used in conjunction with the same auxiliary plate to replace the standard sensitive tint plate. In both cases, diagnostic colour changes are replaced by relative intensity changes.

Aluminium oxides occur widely in soils and are of considerable pedological significance. The ageing of alumina gels, prepared from aluminium chloride and ammonia, into crystalline hydroxides has been investigated using thermal, X-ray, infra-red, and electron-microscope techniques. At room temperature ageing is more rapid at high pH values. The structure of the original gel particles appears to resemble boehmite and ageing causes the formation of bayerite with small amounts of gibbsite. The morphology of the various mineral types is considered and a mechanism of ageing suggested.

By measuring the integrated line intensity on a Philips' X-ray diffractometer in place of the peak intensity and by paying due regard to the ease with which aragonite converts to calcite during cleaning and grinding operations, the proportion of calcite and aragonite in a pure calcium carbonate shell can be determined to within 1% of the total in less than 30 minutes.

Natural cobalt hydroxide is CoO.OH, not Co(OH)2 as has recently been asserted; for this mineral the name heterogenite has priority. Copper, frequently present, may be in solid solution as (Co,Cu)(O,OH)OH, or may be as finely divided malachite; for cuprian heterogenite, the name schulzenite has priority.

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.

A good chemical analysis of an amphibole will give cation numbers that can be correlated in detail with the available lattice positions. The substitions that must be recognized are described. A more rigorous check of the analytical results becomes possible and the sources of error may be indicated.

Kehoeite, a hydrated zinc aluminate-phosphate, produces an X-ray powder diffraction pattern with interplanar spacings similar to those of analcime, viséite, and pollucite. The diffraction maxima appear to be compatible with a cubic (or pseudocubic) lattice with a 13·7 Å. It is concluded that kehoeite is essentially isostructural with analcime and that its framework is composed of linked tetrahedra: (AlO2)−, (H3O2)−, and (PO2)+, as was found to be the case for viséite, which contains (SiO2) in addition. Calculations of the density, the number of oxygens in the unit cell, and the chemical composition are consistent with the structural formula Zn5·5Ca2·5(H2O)32[(Al16P16(H3)16)O96].

The oriented transformation of aragonite to calcite has been studied by X-rays. The [100], [110], and [001] directions of aragonite become [101̄0], [011̄0], and [0001] of calcite. The transformation was completed by a re-orientation of the CO3 groups about the [001] direction of aragonite through an angle of 30°, different rows of CO3 being turned in opposite directions, together with a displacement along the same direction. The layers of Ca ions also are shifted along the basal plane of calcite so that their arrangement perpendicular to the [0001] direction of calcite becomes ABCABCA… instead of ABABABA… as in aragonite.

The linkage of Archimedean polyhedra has been studied to provide trial models for tetrahedrally-coordinated structures such as zeolites. The cuboctahedron, rhombicuboctahedron, snub cube, icosidodecahedron, rhombicosidodecahedron, and snub dodecahedron cannot be used because four edges meet at a corner. The truncated tetrahedron, truncated cube, and truncated dodecahedron have triangular faces, and are unlikely to occur in silicate frameworks because of the instability of 3-rings. The truncated icosahedron and truncated icosidodecahedron have fivefold symmetry and cannot form four-connected frameworks with lattice symmetry. The truncated octahedron and truncated cuboctahedron may be linked either directly, in combination, or with square, hexagonal, or octagonal prisms. There are nine structures of which four are represented by sodalite, Linde A, faujasite, and ZK-5. The other five have the following properties: truncated octahedra linked H(H-S), Fd3m, a 17·5 Å; truncated octahedra linked H′(H-S) and (H-H), P63/mmc, a 12·4, c 20·5 Å; truncated octahedra linked H′(H-S) and (H-H), P63/mmc, a 17·5, c 28·5 Å; truncated cuboctahedra linked O′(S-S), Im3m, a 15·1 Å; truncated octahedra linked to truncated cuboctahedra H′(S-S), Fm3m, a 31·1 Å. The first symbol specifies the linking unit (H hexagon, H′ hexagonal prism, O′ octagonal prism) while the symbols in brackets specify the type of faces opposing across the contact (S square).

An occurrence of kyanite in the inner aureole of a granodiorite intrusion is described from south-western Ghana. Greenschist facies phyllites have been elevated to the amphibolite facies and the regional strike of these country rocks has been disrupted by the intrusion, so that clear evidence is available of the time relationships. It is concluded that the kyanite crystallized as the result of the forceful intrusion of the granodiorite, probably under epizonal conditions.

Powellite, appearing to be of primary late-magmatic origin, has been found associated with analcime, apophyllite, and calcite in a geode in phonolite. Data are: D 4·40, ε 1·984, ω 1·971, a 5·20 Å, c 11·43 Å, CaO 27·8, MoO3 61·8 (av.), WO3 11·4 (av.).

The suitability of monochromators for visual applications in petrographic mineralogy is discussed, and a new and inexpensive instrument employing a graded interference filter is described.

An historical review of the nomenclature of the natural Os-Ir alloys suggests that the most suitable names are: For the cubic alloys, osmiridium (Steffens, 1824), i.e. osmian iridium; and for the hexagonal alloys, iridosmine (Breithaupt, 1827), i.e. iridian osmium, for alloys with 20% or more Ir, and native osmium for the very rare alloys with little or no Ir. Iridosmine may, if desired, be divided into two varieties, nevyanskite and sysertskite, following Rose and Haidinger.