A chemical and petrographic study of charnockites and pyroxene/hornblende-bearing granulites has been undertaken, and the data used in an interpretation of the petrogenesis of these rocks. Major- and trace-element analyses of fourteen rocks are presented, together with majorelement analyses of seven orthopyroxenes, seven clinopyroxenes, two garnets, and three hornblendes. The compositions of the coexisting ferromagnesian minerals are used to obtain estimates of the likely pressure/temperature conditions of equilibration (5-7 kbar and 700±50°C of the various mineral assemblages.

This paper presents an extended version of the local lattice deformation model of solid solutions (J. T. Iiyama, 1974b). It has been assumed previously that a foreign atom fixed in a crystal causes local lattice deformation, which prevents another foreign atom from occupying the deformed zone. The resulting entropy of the solid solution from this model can explain the particular behaviour of ion-exchange reactions observed with alkali and alkali-earth elements in feldspars and in muscovite. The present version assumes that the deformed zone does not prohibit foreign atoms, but that the number of foreign atoms acceptable in this region depends on the total numbers of foreign atoms already fixed in the crystal. The model is applied successfully to explain ion-exchange isotherms observed with Cs, Na, and Li in micas and permits an estimation of the apparent reaction constant of the ion exchange. This is otherwise impossible because of the lack of ideal dilute-solution behaviour in exchange isotherms even at the IO ppm range of the foreign element fixed into the crystal. It is demonstrated that the model can explain the particular behaviour of Li in sanidine.

Optical and microprobe investigations have been made on the metal and silicate portions of four particles > 1 mm extracted from the magnetic fraction of lunar soil bulk sanaple 14162,80. Three of the particles have structures and compositions similar to those encountered in the < 1-mm fraction of this bulk sample. One of the particles shows a complex arrangement of melted metal, unmelted metal, micronorite, and vitroclastic silicate material. The structure of this particle is reported in detail and its structure is explained in terms of preferential melting of metal-phosphide interfaces under the influence of shock events operating on material at a temperature of about 650°C.

The progressive crystallization of dolomite has been investigated in the temperature range of 90 to 410°C by means of X-ray powder diffraction, electron microscopy, and infra-red spectroscopy.

Short-time, low-temperature experiments (≤ 145°C yielded dolomites with a high defect density. In detail, lattice faults can be described as: Random succession of more or less ordered cation domains, producing a long-range mosaic-type disorder; cation ordering may take place along <101̄0> and <112̄0> tilting and dislocation of individual CO3 groups; and irregular interstratification of dolomite layers of different chemical compositions in the crystallographic c-directions.

Dolomites produced in experiments of longer duration are composed of an interstratification of essentially two chemically different dolomite layers, of which the stacking sequence is more perfect than it is at lower crystallization degrees. Both components grow rapidly at the expense of dolomites of intermediate composition. Finally, long-term low-temperature (145°C) experiments produced two independent, coexistent dolomite phases. Within single dolomite layers cations now lie very close to their theoretical positions. CO3-tilting and dislocation decreases markedly.

Hydrothermal runs at temperatures > c. 145°C yielded one single, nearly stoichiometrie, highly ordered dolomite phase. Finally, dolomites synthesized at temperatures > c. 200°C are of an ideal chemical composition and have perfect lattice ordering.

The first known occurrence of kornerupine in Australia is described. The mineral is a minor component of a phlogopite-rich garnet-corundum-spinel metasomatic zone, which cuts mafic and ultranlafic spinel-plagioclase-orthopyroxene-hornblende rocks. The kornerupine-bearing assemblage was formed during the second major metamorphic episode that affected the terrain, probably under low-grade granulite or upper amphibolite facies conditions. Kornerupine appears to have formed at significantly lower levels of P-T than those reached in the terrain during the peak of the second granulite metamorphism.

Ænigmatite occurs as a trace constituent of the Ægirine-Riebeckite Granite of the Liruei Complex, Younger Granite Province of Nigeria. It is enriched in Ti and Mg and depleted in Si, Al, and Ca relative to many other ænigmatites. Relative to coexisting ægirine and arfvedsonitic riebeckite it is enriched in Ti and depleted in Fe3+. Conditions required for formation of the mineral appear to have been high Ti concentration in a peralkaline magma of low T and fo2. The composition of the Nigerian ænigmatite confirms that there is only limited miscibility between rhönite and aenigmatite although in certain circumstances the two may have a paragenetic relationship.

Apjohnite, MnAl2(SO4)4·22H2O, is monoclinic, space group P21/c, a 6·198 (2), b 24·347 (4), c 21·266 (4) Å, β 100·28 (3)° and Z = 4. The crystal structure was determined by means of direct methods applied to X-ray data collected with a single-crystal diffractometer. At the end of the refinement, performed with least-squares method, the R index was 0·039.

The SO4 tetrahedra, Al(H2O)5 octahedra, and MnO(H2O)5 octahedra are connected by a hydrogen bonding system; the only direct connection between polyhedra is by sharing of an oxygen between S(4) and Mn. In the asymmetric unit there are twenty-two water molecules, five of which lie in channels of the structure and are not linked to the cations but only to ligand water oxygens by means of hydrogen bonds.

Powder data indicate a close structural relationship between apjohnite, halotrichite, and pickeringite.

Compositions of nine hydrous aluminium phosphates are considered with respect to the AI, P, and H contents per 8 oxygens, and it is suggested that when the ratio (Al.P)/H is less than 0·11 (or (Al.P2)/H2 is less than 0.01) such compositions do not crystallize. Examples are bolivarite and evansite.

New occurrences of xenolithic alkaline rocks from three East African volcanoes are described. Micro-ijolites and alkali pyroxenites occur in the carbonate-rich tufts and lavas of Mount Elgon; kaersutite-rich pyroxenites and a suite of fenitized basement rocks in the caldera flows of Mount Meru, and apparently unique melanocratic hortonolite nepheline syenites in the central foyaite plug of Mount Kenya. The 87Sr/86Sr ratios indicate mantle origin, and all are enriched in trace elements such as Sr, Nb, and Zr. The xenoliths from Mount Kenya are cumulate equivalents of the glassy kenyte lavas of the mountain; the pyroxenites of Mount Elgon are also cumulates whose predominant titanaugite is of identical composition to that of the host lavas. The contrast between the 'dry' Elgon pyroxenites and the 'wet' amphibole-rich types from Mount Meru is believed to reflect different CO2/H2O ratios in the volatile phase accompanying the alkaline vulcanicity. Strongly alkaline, carbonate-rich suites such as that of Mount Elgon derive from fairly dry alkali-basaltic magma under high CO2 activity by dominant pyroxene fractionation, whereas the mildly alkaline lineage seen in some areas of Mount Meru forms under more hydrous conditions in which amphibole fractionation is important. Mount Meru in addition shows a transition to rock-types typical of the strongly alkaline lineage, and this is reflected in the occurrence of relatively amphibole-poor pyroxenites with the amphibole-rich types.

A plot of seventy-five new analyses of members of the helvine group and fifty-seven analyses from the literature indicates complete miscibility between the Fe and Zn members (danalite and helvine) and between the Fe and Mn members (danalite and genthelvite). The new analyses include essentially pure helvine and genthelvite (for both of which X-ray data are presented) and the nearest approach to pure danalite (86 at. % Fe). Two new localities for genthelvite, the rarest member, are reported.