A new copper arsenate, dimorphous with cornwallite, has been found on specimens from five localities in Cornwall, one in Devon, and one in Cumberland. The name cornubite (from Cornubia, the medieval Latin name for Cornwall) is proposed for the new mineral. Chemical analyses of cornubite and cornwallite agree well with Cu5(AsO4)2(OH)4; sp. gr. cornubite 4·64, cornwallite 4·52. X-ray study suggests that the unit-cell of cornubite has a volume of 228 Å.3 or a simple multiple thereof. New X-ray data for cornwallite (a 17·33, b 5·82, c 4·60 Å., β 92° 13′) agree well with L. G. Berry's except for a. Powder data for both are given.

Zeolites occur at most of the 670 localities studied in the Antrim Basalts, and the ten most abundant species, in order of frequency, are chabazite, thomsonite, analcime, levyne, natrolite, mesolite, stilbite, gmelinite, heulandite, and phillipsite. Gismondine, laumontite, and mordenite are recorded for the first time. Chabazite and thomsonite characterize the upper parts of the lava succession. Below, they are joined by analcime and natrolite and, in some areas where zeolitization is most intense, by stilbite and heulandite, as well. These mineral zones have been mapped, and they probably reflect the temperature distribution in the lavas during zeolitization. Being discordant and clearly superimposed upon the lavas, these zones establish the late age of zeolitization in the volcanic history of Antrim. In places the zeolite zones are missing, and in their place a mineral assemblage rich in calcite, aragonite, quartz, and chalcedony is found. The tholeiite lavas that occupy a small area in north Antrim have an amygdale mineral assemblage different from that in the olivine-basalts, which constitute the remainder of the lava outcrop.

The type locality for erionite has been identified and specimens compared with Eakle's original material. New determinations of the physical properties and a chemical analysis have been made. Correlation of X-ray powder and fibre rotation data with electron diffraction of single crystals has shown that the unit cell is hexagonal with a 13·26, c 15·12 Å., space-group P31c, P¯31c, P63mc, P¯62c, or P63/mmc, giving a calculated sp. Gr. of 2·07 and atomic cell contents (Ca, Mg, Na2, K2)4·5Al9Si27O72.27H2O. A structure is proposed for the aluminosilicate frame, with space-group P63/mmc, which gives satisfactory correlation between observed and calculated structure factors for the X-ray fibre rotation pattern.

The vesicles of an olivine-dolerite that occurs as a small outcrop near Portree in the Isle of Skye contain zeolites and some hydrated calcium silicates. These latter include tobermorite, xonotlite, gyrolite, and what is presumed to be a new member of the tobermorite group. An attempt is made to account for the sequence of crystallization of the minerals.

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.

Minerals approximating to the formulae PtSb2, PtSb, Pt(Sb,Bi), (Pt,Ir)As2, Pt(Ir,Os)2As4, Pd2CuSb, Pd(Sb,Bi), Pd8CuSb3, Pt4Sn3Cu4, and (Fe,Ni)2S have been discovered as fine intergrowths in platinum concentrates from the Driekop mine, Transvaal, South Africa. Conventional ore microscopy also proved the presence of most of the known minerals of the platinum paragenesis. The name geversite is proposed for the phase PtSb2.

The feldspar phenocrysts of some British and Icelandic Tertiary acid glasses have been studied optically and chemically. Six new analyses of the feldspar phenocrysts are presented together with an anorthoclase from a glassy pantellerite. The analysed feldspars and all the other feldspar phenocrysts that have been examined show high-temperature optics, and confirm the results of previous investigations of plagioclase feldspar determinative curves. The relationship of the feldspar phenoerysts to the plagioclase components in the analysed residual glasses conforms to the synthetic plagioelase system, and the crystallization of feldspar in natural acid melts is considered.

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.

Published chemical analyses demonstrate that the nepheline formula should be written KxNayCaz□s-(x+y+z)Alx+y+2zSi16-(x+y+2z)O32, where □ stands for vacant sites. X-ray data are presented for the nepheline phase in four binary systems: Ne-CaAl2O4, Ne-An, Ne-Ab, Ne-Kp. Only in two of these systems do the cell-dimensions change with composition. In the first one, the cell-volume V increases linearly with increasing calcium content; in the last one, two singularities in the curve of V against x divide the phase Na8-xKxAl8Si8O32 into three subphases: subpotassic (0 < x < 0·25), mediopotassic (0·25 < x < 2·00), and perpotassic (2·00 < x < 4·73). Only in the subpotassic range are both high- and low-temperature forms found. Twenty-eight natural nephelines, for which chemical analyses and X-ray data are available in the literature, show that only the potassium content affects cell-dimensions. Although all analysed natural nephelines fall outside the subpotassic range, the re-examination of a Monte Somma specimen studied by Bannister (1931) reveals a few euhedral crystals of subpotassic nepheline in a mediopotassic phase.

The complex kalsilite-bearing melilite-nephelinite from Mt. Shaheru in the Belgian Congo with götzenite, combeite, and kirschsteinite contains yet another new silicate for which the name delhayelite is proposed.

Delhayelite is orthorhombic with a 6·53, b 24·65, c 7·04 Å. Possible space-groups Pmn21 and Pmmn. Weak super-cell with doubled a-axis. Distinct cleavage parallel to (010). Birefringence weak. α ≈ β ≈ γ = 1·532. 2Vα = 83°. Optical orientation: a = α, b = γ, c = β. Sp. gr. 2·60. Chemical composition corresponds to the tentative formula (Na,K)4Ca5Al6Si32O80.18H2O.3(Na2,K2)(Cl2,F2,SO4).

This process has been reinvestigated, mainly with X-rays, using an FeO-containing, fibrous variety (nemalite), and also a nearly pure specimen. The results confirm that the transformation is oriented, the c- and a-directions of the brucite becoming the normals to (111) and (11̄0) in the periclase. There is an intermediate, spinel-like stage; the spinel a-axis is parallel to, and twice as long as, that of the periclase. This stage is especially prominent when nemalite is heated in air or nitrogen, but is shown also by the nearly pure material. The nemalite shows also a further intermediate stage under certain conditions. A new hypothesis is proposed for the dehydration mechanism, in which the number of oxygen atoms per unit volume is ahnost unchanged in those parts of the crystal that are converted into periclase. The process is essentially one of cation migration, and the occurrence of the spinel-like phase is readily explained. Similar mechanisms possibly apply to the dehydration of other lamellar hydroxides and oxy-hydroxides (e.g. gibbsite, kaolinite) and of certain carbonates and other oxy-salts.

The Tomhannock Creek chondrite has been analysed, with the following results: Fe 11·36, Ni 1·69, Co 0·07, FeS 5·26, SiO2 36·88, TiO2 0·135, Al2O3 1·80, Cr2O2 0·30, FeO 14·94, MnO 0·31, MgO 23·81, CaO 1·39, Na2O 0·73, K2O 0·095, P2O5 0·36, H2O+ 0·34, C 0·10; total 99·57. The mineralogical composition is olivine (Fo81), hypersthene (En83), plagioclase (An22), nickel-iron, troilite, chromite, and probably apatite. The density of the meteorite is 3·65.

Tomhannock Creek is not identical with Homestead, nor with Yorktown. Yorktown is a chondrite that appears to have fallen near Yorktown, Westchester County, New York (41° 17′ N., 73° 49′ W.), in September 1869.

The parageneses are given of ten new occurrences of carminite [PbFe2(AsO4)2(OH)2] and eleven of beudantite [PbFe3AsO4SO4(OH)6] in Cornwall and Cumberland, with an account of the alteration of carminite to beudantite and of beudantite to plumbojarosite or to beaverite.

Yoderite occurs as a major constituent in a quartz-kyanite-tale schist, and is a high-pressure phase formed by the reaction Ky + Tc → Yd + Qu. The monoclinic unit-cell, a 8·10 Å., b 5·78 Å., c 7·28 Å., β 106°, space-group P21 or P21m, contains approximately (Mg2·0Ca0·2Fe0·5Al5·3Si4·0O17·6(OH)2·4. The structure appears to be related to that of kyanite, with which the mineral is intergrown; it is not an analogue of staurolite. The three strongest powder lines are 3·50 Å. vvs, 3·03 Å. vs, 2·61 Å. s. Specific gravity 3·39. Subsidiary reflections, similar to those of the intermediate plagioclases, have indices with non-simple fractional values of k. Optical properties are α 1·689 pale Prussian blue, β 1·691 indigo, γ 1·715 light olivegreen, absorption β > α > γ, 2Vγ25°, optic axial plane {010}, γ:[001] ≈ 7° in the obtuse angle β. An interpretation of the colour on the electron-exchange hypothesis Fe2+ ⇌ Fe3+ + e−, is suggested. A kinetic study has been made of the disappearance of the subsidiary reflections in the range 700°C. to 820°C.; further heating to 850°C. produces the metastable appearance of mullite, and at temperatures above 1100°C. the equilibrium anhydrous assemblage indialite + sapphirine appears.