Migmatites are described from the Sillimanite-potash-feldspar Zone of the aureole around the Newer Basic suite of synorogenic intrusions. The lowest-grade migmatites are trondhjemitoid (characterized by the assemblage quartz-plagioclase-biotite) or muscovite-granitoid (quartz-plagioclase potash-feldspar-muscovite-sillimanite-biotite). With increasing grade, a transition occurs to cordierite-granitoid assemblages (quartz-plagioclase-potash-feldspar-cordierite-garnet-sillimanite-biotite), which persist to the highest grades observed, where there are also noritoid migmatites (quartz-plagioclase-orthopyroxene-cordierite-biotite). The trondhjemitoids are texturally simple because the minerals did not undergo dehydration reactions. Textural immaturity and consistently cotectic modal compositions indicate that their leucosomes originated as melts. Scatter of plagioclase compositions suggests that the partial melting occurred in small closed systems. The other migmatites have more fusible compositions, so it is deduced that they also underwent partial melting. Retrograde reaction textures are used to infer the sequence of reactions, involving muscovite and biotite, by which melting proceeded during prograde evolution. Whereas the fugacity of water probably varied among spatially associated trondhjemitoid leucosomes, in the muscovite-granitoids it was constrained to an approximately constant value, at given pressure and temperature, by the buffering effect of the mineral assemblage.

Tacharanite has been re-examined using electron microscopy and diffraction, analytical microscopy, X-ray powder and fibre rotation photographs, and other methods. The composition approximates to Ca12Al2Si18O69H36, and the X-ray diffraction patterns can be referred to an A-centred monoclinic pseudo-cell with a 17·07, b 3·65, c 27·9 Å, β 114·1°, Z = 1. In the true cell b is certainly, and a and c probably, doubled. Small, reversible changes in pseudo-cell parameters occur on heating below 200°C, and parameters found by electron diffraction differ slightly from those found with X-rays, presumably due to shrinkage on dehydration in the high vacuum of the electron microscope. An earlier report that tacharanite changes into a mixture of tobermorite and gyrolite on standing in air is not confirmed. Tacharanite shows some important resemblances to tobermorite, but there are also significant differences.

The alkaline volcanic rocks of Tenerife comprise a compositionally continuous series of ankaramites, alkali basalts, trachybasalts, trachyandesites, trachytes, phonolites, and peralkaline phonolites. Ca-rich pyroxenes occur as phenocrysts throughout the series. They show a limited range of composition from diopside and Ti-rich samite in the basic and intermediate rocks, to sodic sahlite in some phonolites. Features of both the sahlite-aegirine and sahlite-hedenbergite trends are present. Sodic ferrosahlites occur as xenocrystal 'green cores' in phenocrysts from some basic and intermediate rocks. The latter are associated with kaersutite xenocrysts and are similar to pyroxenes in some plutonic xenoliths from Tenerife. During the formation of the 'green cores' conditions were more reducing allowing pyroxene compositions to extend through the range sahlite-hedenbergite.

Aegirine-angite and Ti-rich aegirine are present in the groundmass of some phonolites and in pyroclastic boulders of nepheline syenite. The aegirines are associated with magnesioarfvedsonite and aenigmatite, and it is considered that they crystallized under conditions of low oxygen fugacity.

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.

Z-phase was obtained hydrothermally at 120 °C by decomposition of Al-substituted tobermorite and by reaction of lime and colloidal silica. X-ray and electron diffraction show that the structural element is hexagonal, with a 9·65, c 15·3 Å, and good {0001} cleavage. Reversible water loss and lattice shrinkage occur on heating, the layer thickness (c) decreasing to 12.1 Å at 400 °C. For material in equilibrium with air of normal humidity, the composition is probably between CaO. 2SiO2. 1·7H2O and CaO. 2SiO2. 2H2O; Z = 8 for the structural element. New t.g. and infrared absorption data are presented; the infra-red spectrum closely resembles that of gyrolite, but OH ions attached only to Ca appear to be absent. Conditions of formation are discussed; if Z-phase has any stability field, it is below 120 °C. Crystal structures for Z-phase, gyrolite, and truscottite are suggested, based on the known structure of reyerite.

Wroewolfeite is a new mineral from the Loudville lead mine in Loudville, Massachusetts, U.S.A. The mineral occurs as blue, monoclinic crystals, twinned on {001}, very similar in appearance to posnjakite and langite. It is formed as small isolated pinacoidal crystals (up to 1.0 mm) implanted on covelline and chalcosine. There are three cleavages of equal facility of production. The cell dimensions are a 6.058 Å, b 5.654 Å, c 14.360 Å, β 93° 28′, space group Pc or P2/c. The strongest diffraction lines (in Å) are 7.152 (100), 3.581 (70), 2.628 (35), 2.004 (30), 2.431 (20), 2.379 (20), 2.278 (20). Electronmicroprobe analysis gives CuO 64.22 %, SO3 16.48 %, water by difference 19.30 %. Empirical cell contents are Cu7.88(SO4)2.00(OH)11.76.(H2O)4.22 or Cu4(SO4)(OH)6.2H2O with Z = 2. Wroewolfeite is strongly pleochroic with a light blue, β deep greenish blue, and γ, medium greenish blue. Absorption β > γ ≫ α. The mineral is biaxial with α 1.637, β 1.682, and γ 1.694, 2Vα = 53° The name is for C. Wroe Wolfe, American crystallographer, educator, and philosopher.

Xocomecatlite and tlalocite were found at the Bambollita mine near Moctezuma, Sonora. Xocomecatlite is probably orthorhombic, and an indexed cell based on the powder data gave a 12.140 A, b 14.318, c 11.662. Based on this cell, the empirical contents are Cu36.6 Zn1.7 (TeO4)12.5 (OH)51.6 or Cu3TeO4(OH)4. Tellurate was found both microchemically and by spectrophotometry. Colour rich green (R.H.S. 132A) with pale streak, H = 4. Optically negative with α = 1.775, β = 1.900, γ = 1.920. G = 4.65.

Tlalocite is optically orthorhombic but the cell could not be indexed; only powder data are presented. Chemical analysis showed both tellurite and tellurate and led to the formula

Colour pale blue (R.H.S. 121A) with a whitish streak; H = 1, gummy and sectile. G = 4.55.

Plotting stability fields for various Te species at 25°C in terms of Eh and pH showed that TeO42−.aq can exist in nature over a wide pH range, but only under extreme conditions of oxidation.

Major- and trace-element analyses of the clinopyroxenes and biotites from the ring-intrusions of Centre III in the Tertiary igneous complex of Ardnamurchan are presented. It is shown that there are systematic differences in mineral chemistry between the eucrites, the gabbros, and the dolerites, and in particular the clinopyroxenes show an iron enrichment trend that is similar to that found in fractionated tholeiitic intrusions. The minerals from the intcrmediate rocks, the tonalite and quartz monzonite in the centre of the complex, do not show the further iron enrichment expected if these rocks had formed by continued fractionation of basic magma. On the basis of the chemistry of the clinopyroxenes and biotites, the intermediate rocks are interpreted as hybrids formed by the remelting and assimilation of country rocks into basic magma.

A minor picritic body at Suisnish Point, Isle of Skye, is described. The mass has a dyke-like form, and is rhythmically layered. Cryptic layering, however, is absent. From a study of the field relations, contacts, metamorphic aureole, and other physical features, it is concluded that the mass crystallized in situ (i.e. it is a true dyke) and is not an upfaulted block of pre-existing igneous rock. The main physical and chemical features of the layered units and their mineralogy are described. The problems of generating horizontal rhythmic layers in a relatively small, essentially vertical, planar intrusion are discussed. It is concluded that the surrounding country rock was maintained at a moderate temperature during, and after, intrusion of the picritic magma and that this allowed a combination of gravity settling and magma flow currents to produce a cumulate rock with characters normally only observed in much larger intrusions.

The composition of the various phases present in the rh6nite-bearing leucite basanites of the southern part of the Sillon Houiller district have been determined with the electron microprobe. Clinopyroxenes show strong progressive enrichment in Al2O3 and TiO2, maximum values being 13 % and 6 % respectively. These extreme compositions are comparable to others found in feldspathoidal lavas from other provinces, and can be explained by the low silica content of the liquids they crystallized from, and high cooling-rates. Rhönite composition is similar to those previously determined in various terrestrial occurrences. The chemical compositions of the lavas differ from those of basanites, and are intermediate as far as Ca, Al, and Si contents between basanites and melilite-bearing basic lavas. The presence of rhönite can be explained by bulk composition, but is not a consequence of a particularly high Fe and/or Ti content. Xenoliths are absent from these lavas, so that there is no petrographic indication of possible contamination. It is tentatively concluded that the high K/Na ratio is primary.

Iraqite, a new mineral of the ekanite group from northern Iraq, has the composition (Ln1·33 Th0·66x0·15) (K1·07y0·93) (Ca3·49 Ln0·35 Na0·16) (Si15·69 Al0·27) (O39·93 F0·07) where x = U, Pb, Zr, Fe, Mg, and Cu, and y is presumed to be vacant sites. It occurs in granite in contact with dolomitic marble. The colour is pale greenish yellow; H 4½ Dcalc 3·28 and Dmeas 3·27 (Berman balance), both corrected for minor impurity and non-structural water. Optically it is uniaxially negative with ω 1·590 and ε 1·585 though some sections show anomalous extinction up to 7°. Space group is P4/mcc with a 7·61±0·01 and c 14·72±0·02 Å. Strongest lines of the indexed powder pattern are 5·28(100), 3·31(100), 2·64(100), 7·36(80), 3·38(80), 3·40(60), 2·7(40), 7·62(30). Thermal data are given.

Carlfriesite is a new species found in relative abundance at the Bambollita (now La Oriental) mine in the Sierra La Huerta near Moctezuma, Sonora. Colour primrose yellow (R.H.S. 4B) with pale yellow streak. H = 3½, Dmeas = 6·3, Dcalc = 5·93. Fair cleavage on {010}. Monoclinic with a 12·585 Å, b 5·658, c 9·985, β 115° 35′. Space group Cc or C2/c. Strongest lines are 3·167 (10), 3·082 (9B), 5·063 (6), 2.832 (6), 3·369 (4), 4·825 (3), 2·698 (3), and 4·o89 (2). Feeble pleochlroism in pale yellow with γ > α = β α = 1·982, β = 2·095, γ 2·19 2Vα, = 79° calc. Occurs with cerussite and chlorargyrite in an oxidized assemblage derived from hessite, galena, and bornite.

Examination of some pyroxenite nodules from the Jagersfontein kimberlite shows that they have suffered variable deformation followed by different degrees of recovery. Most interes~ting of the nodules is the 'diallage rock', which consists of highly sheared and broken lamellar crystals of diopside containing exsolved enstatite. Petrographic evidence indicates a pre-tectonic exsolution of enstatite and a syntectonic exsolution of pyrope-almandine from enstatite. Deformation occurred in the mantle, prior to incorporation of the nodule in the kimberlite. Compositions of pyroxenes from the diallage rock suggest it re-equilibrated at a temperature of 1000° and at a pressure of about 35 kb. Olivine and phlogopite, accompanied by serpentine, occur only in broken kink-bands in the diallage rock and they are considered to be of secondary origin, precipitated from kimberlite magma at temperatures near 700°

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.

Creaseyite was first noted in specimens from Tiger, Arizona, and was then found at Wickenburg, Arizona, and Caborca, Sonora, prior to description. It is an oxide zone mineral occurring with wulfenite, willemite, mimetite, chrysocolla, wickenburgite, and ajoite. The composition is [Cu2Pb2(Fe,Al)2Si5O17-6HaO]. Colour Agathia green (R.H.S. 142B) with pale streak, H = 2½, Dmeas = 4.1, calc. 4.01. Crystals are orthorhombic with a 12.483, b 21.395, c 7.283. Z = 4.2Vγ 69° meas; α 1.737, β 1.747, γ 1.768.

A metallographic investigation of macro- and micro-structures, supported by microprobe examination, has been made on similarly sized (< ca. 200 g) individual Cañon Diablo meteorites of rim or plains type. Plains type specimens show heat alteration zones of the ablation type. They are extensively cracked in a brittle manner and in some instances the cracks are penetrated by ablation melt product. In all cases the cracks are now penetrated by terrestrial corrosion. Cohenite and schreibersite are cracked in a brittle manner. By contrast the rim type specimens are remarkably free of internal cracking or corrosion penetration. Instead the cohenite, schreibersite, taenite, and kamacite are transected by slip faults or shear displacements along the line of which all phases appear to have slipped in a non-brittle manner. These specimens have all been subject to shock loading and particular attention is paid to the effects of shock on sphalerite, on cloudy taenite, and on martensitic plessite.

Plains specimens have broken from the original projectile in a brittle manner well above the earth's surface. Rim specimens have been scabbed from the rear of the projectile as it penetrated the earth's surface. Some of the rim specimens show signs of being heated by the blast of the crater-forming explosion.

Large albitite bodies associated with explosive brecciation, fenite aureoles, intrusive carbonate rocks, olivine dolerites, and copper mineralization are described from the Dead Sea rift region in the south-eastern Sinai Peninsula. The main carbonate phases comprise breunnerite and dolomite with actinolite the main phase in the fenites. Field and isotopic evidence indicates that the intrusive carbonate rocks are of carbonatitic origin. The cogenetic, almost monomineralic main phases can be attributed to fractional crystallization and liquid immiscibility acting on a highly gascharged, slow-cooling gabbroic magma. The complex, which is probably of Cretaceous (or older) age, appears to be related to early continental separation along the Dead Sea branch of the African rift system. The porphyry-type copper deposits resemble others that are located along crustal accretion (Iceland) or subduction (Chile) zones.

The crystal structure of schairerite from Searles Lake, California, has been determined employing X-ray diffraction data collected on a single-crystal diffractometer. The crystal structure was refined by least-squares methods employing isotropic thermal parameters to a final R index of 0·07 for 2536 independent observed reflections. The cell content is 3[Na21(SO4)7F6Cl]. The space group is P31m with a 12·197 A and c 19·259 Å. Schairerite exhibits a marked sub-cell (a 7·042 Å, the same c axis and P3m1 symmetry), which may be related to the unit cell of sulphohalite when described in a hexagonal lattice.

The crystal structure of schairerite may be considered as consisting of seven sheets of Na+ ions perpendicular to the c axis. These sheets are connected to each other .building up a three-dimensional framework. The Na+ ions in these sheets are arranged in an array built up of hexagons and triangles. Sulphur atoms lie in the sheets at the centres of each hexagon, the halogen atoms lying between the sheets midway between the centres of two triangles. A comparison with sulphohalite shows that the close lattice analogies may be related to a similar atomic arrangement. Apart from the differences in chemical formula (F:C1 ratio 1:1 in sulphohalite), the main difference in the structural framework consists of the unequal number of Na+ sheets (six in sulphohalite) and in the SO42− tetrahedra orientation.

An electron-probe microanalysis of tetrahedrite occurring together with the latest-deposited pyrite-cinnabar association in the Chiprovtsi lead-silver deposit yielded more than 16 wt. % Ag and more than 18 wt. % Hg. X-ray powder examination established an extremely large unit-cell edge, a 10.64±0.01 Å. Vickers microhardness 223 to 237 kg/mm2. The chemical formula derived on the basis of the analyses made is quite near to Cu6+(Cu+, Ag+)4(Hg,Zn)2(Sb,As)4S13. There is not any antiparallelism between Ag and Hg in tetrahedrite. The name proposed for all stages of simultaneous isomorphic replacement along the Cu+-Ag+ and Cu2+-Hg2+(Zn2+,Fe2+) directions is argentian mercurian tetrahedrite. The upper limits of the Ag and Hg content are expected to be Cu6Ag4Hg2(Sb,As)4S13. It is the six copper atoms (Cu4+;Cu22+), sited in the Laves’ polyhedra, that are replaced by Ag+ and Hg2+ respectively.