Mineralogical and chemical data are presented on an intrusion of a hypersthene gabbro body into coarse-grained noritic cumulates of the critical zone, which occurs at the margin of the Rustenburg Layered Suite of the Bushveld Complex. Two types of contact relations are found between the above two rock suites: (1) a clearly cross-cutting contact is observed on the southern margin of the hypersthene gabbro body close to the interface between the layered suite and the floor rocks; (2) a diffuse heterogeneous contact is found on the north-western limb of the body which is further into the complex. Field observations and chemical data suggest that, at the time of the hypersthene gabbro injection, the surrounding cumulates were above ambient temperatures. The difference in the contacts described above is probably related to the prevailing temperature gradient at the time of emplacement. The cumulate rocks further into the complex were at a higher temperature than those closer to the margin.

Trace element chemistry and phase relations in the basalt tetrahedron indicate that the hypersthene gabbro is genetically unrelated to the cumulate rocks which it intrudes. The body probably represents an offshoot of the magma from which the upper zone of the Rustenburg Layered Suite crystallized.

Subsolidus diopside compositions and coexisting diopside and liquid compositions which are also in equilibrium with anorthite and forsterite in the system CaO-MgO-Al2O3-SiO2 were determined by X-ray diffraction and by electron microprobe in samples equilibrated at 1 bar and at 7 kbar. Along with previous data from the literature and using a recently published grid relating diffraction peaks to composition, results from both techniques are satisfactorily reconciled. At 1 bar, diopside composition (moles, Di = CaMgSi2O6, En = Mg2Si2O6, CaTs = CaAl2Si2O6) in equilibrium with anorthite, forsterite, and spinel (analogous to alkali basalts) are close to Di79CaTs20En1 and those in equilibrium with anorthite, forsterite, and pigeonite (analogous to tholeiitic basalt) are close to Di75CaTs3En22. At 7 kbar the equivalent compositions are Di69CaTs28En3 and Di69CaTs26En5 respectively.

In the system CaO-Na2O-MgO-Al2O3-SiO2, electron microprobe analyses of augites and liquids at 1 bar confirm the changes expected in the loci of liquids and show that the low Na2O (< 0.50 wt.%) augites are similar to those in CaO-MgO-Al2O3-SiO2. At 7 kbar the orthopyroxene field has expanded sufficiently and augite was not encountered in the limited range of samples studied.

In remelted rocks the augite compositions at 1 bar are similar to the compositions of augites in low pressure effusive rocks. At 2–15 kbar, the available data in the literature for dry basalts show that experimentally recrystallized augites are very sub-calcic and very aluminous, and no natural equivalents exist in plutonic gabbros or in ophiolitic rocks. This discrepancy is not resolved but either the experimental pyroxenes are metastable or the pyroxenes presently in the rocks are not the pristine compositions.

Rock samples from the various metabasic hornfelses of the Land's End granite aureole were analysed for major elements by X-ray fluorescence analysis and for rare-earth elements (REE) by instrumental neutron activation analysis (INAA). The REE patterns of the unaltered dolerites of the area seem to be analogous to those of the alkali basalts, taking into account a slight mobilization of the light REE during low-grade metamorphism.

The REE content of the metabasic rocks of the aureole has increased relative to that of the unaltered dolerites due to the introduction of REE, along with K, from the granite by the action of hydrothermal solutions. The parallel increase in REE with the increase in K is demonstrated.

The metasomatic hornfelses of igneous origin form two groups showing slightly different REE patterns and different rates of increase in REE content. The REE patterns of the two groups show a Eu anomaly increasing with the increase in REE content for the first group and decreasing with the increase in REE content for the second group, A qualitative model of the distribution of the REE in the metabasic aureole rocks is given.

Particle morphology can result in very pronounced effects of crystallinity on the Mössbauer spectra of lepidocrocite. Such effects can noticeably increase the quadrupole splitting of poorly crystallized paramagnetic lepidocrocites, making it necessary to fit two doublets of different quadrupole splittings to Mössbauer spectra of such samples, and may lower the onset of magnetic ordering from the bulk Néel temperature of 77 ±1 K to about 50 K.

At 4.2 K, distributions of magnetic hyperfine fields with a limiting upper field of 460 kOe are observed. The contributions of lower fields to such distributions increase with decreasing crystallinity, producing asymmetrically broadened resonant lines.

An unusual form of sector zoning has been recorded in some Lewisian zircons. The sectors lie in a plane cut perpendicular to the c-axis and are observed as variations in the intensity of cathodoluminescence, and in trace-element concentrations. Sectors radiating from the centre of growth out to the {100} faces exhibit low-intensity cathodoluminescence and are enriched in Y and depleted in Hf and Zr. Those radiating to the {110} faces are brightly luminescent, slightly enriched in Hf and depleted in Y. X-ray diffraction data, and comparison with previous studies of zircons, suggest that the sectors vary slightly in crystallographic orientation, such that the boundaries between sectors form discontinuities in the structure.

Fine radiating groups of columnar aragonite crystals occur in a basaltic pipe at Kulnura, New South Wales, associated with calcite in habits varying from simple rhombohedra to complex spherulitic groups. It is proposed that the presence of impurities, especially magnesium, induced the crystallization of aragonite and was also responsible for the variety of calcite crystal habits present. Two distinct growth environments are indicated: steam-explosion breccia pipes containing aragonite and calcite showing an advanced stage of spherulitic growth; and vesicles with calcite in varying stages of spherulitic growth. This paper presents a preliminary study based on available material and on observations made in situ while access to the locality was still possible.

A miscibility gap exists between titansahlite and late-stage titanian aegirine in a teschenitic sill, with coexisting kaersutite plotting between them. A second series of titansahlite-sodian-ferrosahlite-aegirine-augite is continuous.

Retzian-(La), ideally, Mn2La(AsO4)(OH)4, is a new rare-earth analogue of retzian and retzian-(Nd). It was found associated with willemite, calcite, and franklinite, in the Stealing Hill Mine, Ogdensburg, Sussex County, New Jersey, USA. Retzian-(La) is orthorhombic, space group Pban, with a = 5.670(7), b = 12.01(1), and c = 4.869(8) Å. The strongest lines in the X-ray powder diffraction pattern are (d,I/I0,hkl): 3.51 80 111, 2.715 100 131, 1.848 50 061, 1.456 40. Microprobe analysis yielded MnO 25.2, MgO 3.7, ZnO 1.2, As2O5 26.5, La2O3 10.6, Ce2O3 8.8, Nd2O3 8.2, Pr2O3 5.1, Sm2O3 2.2, Y2O3 2.5, H2O [7.7], sum = 101.7 wt. %, corresponding to an La-dominant member of the retzian series.

Retzian-(La) forms 0.5 mm euhedral crystals composed of the forms {001}, {010}, {110}, and {150}; the crystals have pseudohexagonal habit. It is reddish-brown, with vitreous luster, no cleavage, density > 4.2 g/cm3. Optically, it is biaxial, positive, 2V = 82° with α = 1.766, β = 1.773, and γ = 1.788. Dispersion is strong, r > v; pleochroism is very weak; orientation is X = c, Y= b, Z = a; absorption is Z > Y > X.

Caratiite is a sulphate-chloride of potassium and copper with ideal formula K4Cu4O2(SO4)4MeCl (where Me = Na and/or Cu); it formed as fine green acicular crystals in lava of the 1869 eruption of Mt. Vesuvius, Naples, Italy. Caratiite is tetragonal, space group I4; a 13.60(2), c 4.98(1) Å, Z = 2. The strongest lines of the powder pattern are [d Å, I, hkl]: 9.61 100 (110); 6.80 80 (200); 4.296 60 (310); 3.015 100b (420,321); 2.747 70 (411); 2.673 60 (510); 2.478 60 (002); 2.388 70 (431,501); 2.281 60 (600). The mineral is uniaxial positive, ω 1.598, ɛ 1.711; it does not fluoresce under either short- or long-wavelength ultra-violet light. The specific gravity is 3.0 (meas.) and 3.22 (calc.).

The crystal structure of caratiite, K4Cu4O2 (SO4)4MeCl (a 13.60(2), c 4.98(1) Å, Z = 2) was solved in space group I4 from single crystal data, and refined to R = 0.035 for 654Fo > 6σ(Fo). The atomic arrangement is characterized by Cu2O(SO4)2 chains parallel to [001], with Cu in (4 + 1) co-ordination and O surrounded tetrahedrally by four Cu atoms. These chains are interconnected by K atoms to a framework, the channels of which house the Me and Cl atoms. The nature of the Me atoms is not completely clear; most probably the position is half occupied by Cu, fully occupied by Na, or occupied by a mixture of the two.