Zapatalite, Cu3Al4(PO4)3(OH)9·4H2O, was first found at a small prospect north-west of Cerro Morita, 27 kilometers south-west of Agua Prieta, Sonora. It occurs in silicified and brecciated limestone with libethenite, chenevixite, beaverite, alunite, and pseudomalachite.

Zapatalite is pale (faience) blue with pale blue streak; H = 1½, G = 3·016±0·026. It is soluble in cold dilute acids and decomposed by 20% KOH. Duplicate analyses on samples of about 9 and 15 mg gave CuO 27·92, 25·77%; Al2O3 20·16, 20·26%; P2O5 20·69, 22·51%; H2O 15·46, 15·79%; insol. (baryte and quartz), 15·46, 15·79%. This leads to the formula Cu3Al4(PO4)3(OH)9·4H2O.

The cell can be indexed as tetragonal with a 15·22Å, c 11·52Å, and a volume of 2669Å3. If Z = 6, empirical cell contents are Cu19·4Al22·8(PO4)17·6(OH)55·422·2H2O, and the calculated G = 3·017. Strongest lines of the powder pattern are 7·62 (10), 11·60 (10), 5·75 (7), 6·82 (7), 3·04 (5), 2·53 (5), 2·95 (4), and 2·88 (4).

Pale green in thin section with feeble dichroism in green, with ε > ω. The good basal cleavage is a length slow direction. Indices for Na-D are ε = 1·635, ω = 1·646. Usually uniaxial (—), but may be biaxial (—) with variable 2 V.

Named for Emiliano Zapata (1879–1919), a popular hero of the Mexican revolution. Type specimens to be left with British Museum (Natural History) and the University of Arizona.

The person after whom forsterite was named has been confirmed as Jacob Forster (1739–1806), a mineral collector and dealer of London. The discovery of palladium and rhodium by William Hyde Wollaston and of iridium and osmium by Smithson Tennant appears to have been made on crude platinum ore from South America supplied by Forster.

Polarized spectra (2000 to 25000 Å) have been obtained for fifteen analysed trioctahedral micas covering a wide range of compositions, and including four phlogopites, nine biotites, and two lepidomelanes. Three main contributions to the absorption have been noted: charge transfer from oxygen to ferrous iron throughout the visible and near ultraviolet, charge transfer from ferrous to ferric ions at the red end of the visible spectrum and internal d-d transitions of ferrous ions in the near infrared.

Substitutions in the brucite layer (especially Ti) cause the O → Fe2+ band to broaden, and thus to encroach on the visible region for vibration directions in the plane of the cleavage flake. The transmission window between these bands is further blocked by the Fe2+ → Fe3+ charge-transfer band, which is polarized in the plane of the flake. The overall effect is to produce very strong absorption throughout the visible region for (β, γ) vibration directions, and relatively weak absorption for α, i.e. the observed very strong pleochroism of biotite.

Many features of the spectra of chlorite, amphiboles, and tourmaline, which contain octahedral ions in brucite-like sheets, strips, and fragments respectively, may be interpreted by analogy with biotite.

Two types of solid solution effect are described: substitutional broadening, which is responsible for the extension of the O → Fe2+ band into the visible region in biotites and aluminous ortho-pyroxenes, and substitutional intensification, which permits in solid solutions transitions that are forbidden by the conventional selection rules.

The crystal structure of dundasite from Gonnesa (Italy) was solved by a three-dimensional Patterson function computed using intensity data collected photographically by the Weissenberg method, and refined by successive Fourier maps and least-squares cycles to an R index 0·.066 for 505 independent observed reflections.

The chemical formula resulting from the structural analysis is PbAl2(CO3)2(OH)4·H2O. The mineral is orthorhombic, space group Pbnm, with a 9·08 Å, b 16·37 Å, c 5·62 Å. The dundasite structure consists of a three-dimensional framework of coordination polyhedra around Pb and Al. Pb ions are coordinated by nine oxygen atoms with distances ranging from 2·53 to 2·91 Å. Al ions show the usual octahedral coordination with average Al-O distance 1.90 Å. C-O mean distances are 1·28 and 1·27 Å for the two non-equivalent CO3 groups. The water molecules are not coordinated by the cations.

Retrograde metamorphism of gneisses and pegmatites leads in part to the destruction of feldspar and its replacement by late-stage lobate myrmekite and muscovite. Reactions promoted by retrogression suggest a range in volume of quartz production that may supplement that developed by exsolution and lead to deviations from the strict proportionality relationship suggested by previous workers. There is no need, however, to propose that quartz in myrmekite originates by constriction of pre-existing quartz within exsolved albite.

Aggregates of clinopyroxene in some doleritic lavas have external outlines strongly reminiscent of garnet crystals. They cannot be satisfactorily identified either as Upper Mantle fragments or as cognate synneusis aggregates, and it is suggested that they may have developed by inversion from original garnets, which crystallized at very high pressures. Neither morphology nor composition can provide conclusive proof of their original nature, but there is circumstantial evidence from the presence of an unusual inclusion suite in basalts nearby. The commonest phases are zircon and corundum, minerals more usually found in kimberlites than in basalts. Corundum in kimberlite inclusions is almost invariably accompanied by calcium-rich garnet, which adds some significance to the suggestion that these clinopyroxene aggregates are pseudomorphing original garnet.

The oxidation of amosite, crocidolite, and biotite has been determined at temperatures up to nearly 900 °C under both a vacuum (10−2 mm Hg) and oxygen (10 and 600 mm Hg). Infrared spectra gave the loss of constitutional hydroxyl under these conditions. The loss of tensile strength of the amphiboles with increasing temperature seems to be due to thermal decomposition. For the three minerals oxidation takes place progressively over a broad temperature range. Under vacuum there is a certain temperature above which the ferric iron previously formed is reduced; this temperature corresponds to the completion of the loss of hydroxyl. The crocidolite anhydride in the literature is most probably an oxycrocidolite formed by dehydrogenation, the truly dehydroxylated zones being amorphous.

This paper gives a revision and expansion of an earlier interpretation of the thermal expansion behaviour of the framework silicates. The partially-collapsed and ideal fully-expanded structures of quartz, cristobalite, and sodalite are characterized by the geometric relationship between the angle of rotation of their tetrahedra from the ideal fully-expanded state, their cell parameters, and the length of the tetrahedron edge. Their thermal expansion behaviour is interpreted as due mainly to the effect of the rotation of the tetrahedra towards the fully-expanded state modified by anisotropic thermal motion of the framework oxygens and distortion of the tetrahedra from a regular form. With the leucite and sodalite groups the significance of the interframework cations is discussed.

X-ray, density, refractive index, and optical absorption measurements have been made on metamict Ceylon zircons. The appearance of a previously reported anomalous optical absorption spectrum in low Ceylon zircons has been associated with small particles of cubic or tetragonal zirconium dioxide in a radiation-damaged zircon lattice, in both heated and unheated stones. No evidence of a previously reported second phase was detected in intermediate Ceylon zircons.

Homogeneous glasses for the use as standards in electron-probe microanalysis were prepared as an alternative to natural minerals, oxides, and pure minerals. Homogeneity was achieved by careful grinding, mixing, and fusion of powders of known composition. Fusion was carried out under vacuum using a molybdenum boat. This method avoided bubbles and contamination and made it possible to achieve temperatures high enough for final mixing to occur during the fusion process. Nine glass beads each containing six to seven oxides were subjected to careful micro-probe examination. A statistical analysis of the results showed that for each element there was no significant difference in composition between the spots measured. As the analysing spot was of diameter 0·8 µ, this showed that the glasses were homogenous on a sub-micron scale.

Rapid, accurate silica determinations have been made titrimetrically following decomposition by HClO4-HF in a ‘Teflon’ vessel, the volatilized silicon tetrafluoride being precipitated as K2SiF6 in a HF-KF-glycerol-alcohol mixture. After filtration and washing with alcohol the precipitate is dissolved in boiling water, then titrated with NaOH. This method has many advantages over conventional gravimetric or spectrophotometric procedures.