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.

This hydrothermal process has been studied using single crystal X-ray methods. A crystal of tobermorite (Ca5Si6O22H10), treated with water at 380° C. and 250 atmospheres, gives a preferred orientation aggregate ofxonotlite (Ca6Si6O17(OH)2), together probably with unoriented silica. The relationship of orientations of product and starting material was established. The change occurs without intermediate dehydration of the tobermorite to the 9·35Å. state. The structural basis of the relationship is discussed, and it is compared with those already reported for the transformations of tobermorite into β-CaSiO3 and of xonotlite into β-CaSiO3. A simple experimental procedure for the single-crystal study of hydrothermal reactions is described.

The technique of X-ray absorption microspectroscopy is described, with particular reference to the determination of calcium in a hydrogel formed in minute amounts in cavities in larnite. The method, which is applicable to other elements, enables chemical data to be obtained from selected small areas in a normal petrological thin section.

The paragenesis of a suite of hydrothermal minerals (sulphides, baryte, rhombohedral carbonates, quartz, sericite, and chlorite) at four mines in this district is discussed. Of particular interest are the conversion of pyrrhotine to marcasite, which is shown to take place by loss of iron, the replacement of blende by chlorite, and the possible formation of primary goethite. The occurrence of gudmundite is recorded for the first time in the British Isles.

An elongated boss of alkali dolerite is described having a NW. trend and measuring 800 m. by 250 m. Two main rock-types occur, an ophitic feldsparrich analeime-olivine-dolerite or leucodolerite and a tesehenite with subhedral pyroxene. The second type is intrusive into the first but the two are associated in vertical veins. Both show local banding and analcime-nepheline-syenite forms a differentiate of both. Finer grained olivine-rich dolerite resembling the crinanites of Jura occurs at the NW. extremity of the boss and probably represents the original magma. All four types have been analysed and are thought to be the products of normal crystal fractionation with slight absolute iron enrichment. The boss was apparently headed not far above the existing exposures and is considered to be of Tertiary age. The pyroxene and olivine of the leucodolerite have been separated and analysed.

The gels prepared by adding ammonium hydroxide rapidly to ferric chloride solutions to various pH values are shown to consist of amorphous material and crystalline goethite ; no other iron oxide was definitely identified in the present experiments, although this does not preclude other oxides being present in gels prepared under slightly different conditions. The goethite grows as acieular crystals on ageing at all pH values, but the rate of growth is greater at higher pit values. The exothermic peaks appearing on differential thermograms of such gels are apparently due to coalescence of extremely minute hematite particles to give larger particles, the sharpness of the peak indicating to some extent the size of the original hematite particles. These observations are related to data for other iron oxides, and the morphology of ferric oxide polymorphs under the electron microscope is considered.

Psilomelane has been shown to be orthorhombic with a 8·254, b 13·40, c 2·864 Å. by the application of Lipson's method. The indexing of powder photographs of psilomelane , where R″ includes the bivalent metals Mn, Ba, Ca, Mg, Co) indicates the space-group P21212 (D22) with one molecule per unit cell. Indexing of powder photographs of psilomelane is not satisfactory with Vaux's axes. Fermor's ‘psilomelane’ is cryptomelane, which is tetragonal with a 9·822, c 2·858 Å. Cryptomelane (KR8O16, where R stands for Mn in different valency states, partly replaced by other cations) is body-centred tetragonal with one molecule per unit cell. Fermor's stalactitic ‘psilomelane’ has an inner dull core of cryptomelane and an outer fine-grained crust of pyrolusite in each needle-shaped body.

A number of secondary minerals have grown in recent years in a part of the Billingham anhydrite mine, by evaporation of water from the Upper Magnesian Limestone, and include some unusual species, the most interesting of which is thought to be ilsemannite.