The location and some characteristics of nine veins containing nigerite are reported. These veins are part of the province of tin-tantalum veins of central Amapá. They are intrusive in andalusite schist and commonly consist of pegmatite in the centre and of quartz-mica rock at the margins. The nigerite can occur in the pegmatite as well as in the quartz-mica rock; its presence in a sample of quartz-sillimanite rock is also mentioned. In both pegmatite and quartz-mica rock, the common associated translucent heavy minerals are cassiterite, tourmaline, chrysoberyl, and occasionally andalusite, sillimanite, and garnet. Associated minerals in the quartz-sillimanite rock are cassiterite and chrysoberyl. Nigerite and cassiterite commonly occur together but are not found in the presence of gahnite. A possible explanation for this is given.

The nigerite of Amapá occurs as thin hexagonal plates, transparent and golden brown, amber-yellow or colourless, with diameters from microscopic up to a few millimetres. The sizes and the optical sign of this nigerite are the same as those of Nigeria and of Siberia, whereas Portuguese nigerite occurs in very fine grains and is mostly optically negative. The existence of alluvial nigerite is reported.

Monoclinic BiVO4, well known as a high-temperature compound, has been found as a mineral at Yinnietharra and subsequently in specimens from five further W.A. localities, Londonderry, Wodgina, Menzies, Westonia, and Corinthia. At the type locality, the mineral occurs on garnet in a beryl-bearing spessartine pegmatite associated with bismutite, bismutoferrite, and other pegmatite minerals.

Clinobisvanite occurs as yellow powder and orange aggregates and plates to 0·1 mm, is commonly intergrown with bismutite, and frequently associated with its polymorph pucherite. It has a yellow streak, earthy to subvitreous lustre, is very soft with perfect {010} cleavage, D calc. 6·95, transparent in very thin cleavage flakes, and shows multiple twinning with cross hatching, strong dispersion and n calc. 2·63.

Space group I 2/a, a, 5·186, b 11·708, c 5·100 Å, β 90° 26′ refined from powder data. An electronprobe analysis gave Bi2O3 69·88, V2O5 27·63, PbO 1·34 sum 98·85. Cell content 4[BiVO4] with minor substitution of Pb for Bi. All measurable data agree with earlier work including a prior description of the mineral from Mozambique.

Type material is preserved in the government collections at the Government Chemical Laboratories, W.A.

The positions of all the atoms including hydrogen have been found by a partial three-dimensional single-crystal neutron-diffraction study in which about one-third of the reflections in the reciprocal sphere to 1·5 Å were measured. The hydroxyl group is perpendicular to the plane of the silicate sheets. The fluorine content of this phlogopite is enough to occupy 25 % of the (OH, F) sites. Site occupancy refinement suggests that there is a small deficiency of hydrogen at the remaining sites and that the two crystallographically different octahedral sites are fully occupied by the same proportions of Mg, Ti, Fe, and Ca.

The Bratteggdalen granogabbro, a relict mass in the Caledonian amphibolites of Vestspitsbergen, shows a series of amphibole development reflecting its thermal history. A brown Ti-rich hornblende occurs as a late magmatic mantling of pyroxene. Low-grade metamorphism (greenschist facies) was accompanied by the development of actinolite from pyroxene; subsequent amphibolite facies metamorphism saw the development of an alkali-rich, blue-green hornblende. The chemical changes in the amphiboles are a succinct illustration of those found in progressive regional metamorphism.

Electron microprobe and textural data are used to deduce a crystallization history for plagioclase in the Grand Manan Island (Canada) diabase sheet. The plagioclase crystals consist of a prominent core (An79-67) surrounded by a distinctly more calcic zone (An82-76), which grades into a normally zoned mantle (An73-40). This zoning pattern is interpreted as reflecting the elevation of a dry diabase magma from at least 10 to 20 km to near surface conditions.

A detailed petrographic and microprobe study was carried out on atoll-shaped garnets from the aureole of the Ardara pluton, in which regionally metamorphosed rocks have been affected by thermal metamorphism. Textural evidence showed that the atoll garnets are formed by replacement mainly by biotite, some plagioclase, quartz, and opaques, and may proceed from the garnet interior towards the margins, or from the margins into the core. Core replacement occurs mainly in those garnets enclosed by quartz or quartz-rich matrix.

Microprobe analyses are presented of garnets in different stages of atoll formation. Compositional profiles at the garnet margins show abnormal (reversed) zoning with increase in MnO and Fe2O32, marked decrease of CaO, and decrease of MgO towards the extreme edge. With decreasing width of the atoll rims, there is generally an increase in MnO and to a lesser extent Fe2O3, a decrease in CaO; MgO is variable. The microprobe data support the textural observations and a model for atoll formation involving prograde resorption (i.e. garnet replacement during temperature increase) is presented.