The Mineralogical Society celebrated its 50th Anniversary in 1926; this address attempts to summarize the substantial developments in the subject over the past 50 years and looks ahead to the future. Up to 1926, only the techniques of goniometry, optical investigation of non-opaques, and classical chemical analysis had been fully exploited. X-ray crystallography, though already 14 years old, had made little impact but was to advance with great rapidity to achieve, for example, the modern conception of silicate structure by 1934. The insight into the atomic structure of minerals provided by this technique has been central to the advancement of the subject. The powder camera and more recently the counting diffractometer have become the chief determinative tools, though microscopy is still important. Diffractometry with a tied computer has greatly speeded up structural work. Advances in electron microscopy may soon make it possible to produce direct images of atomic structure. Meanwhile wet-chemical procedures have largely given place to spectroscopy (optical emission, X-ray, and atomic absorption), to the electron microprobe and to various still more advanced techniques, including the investigation of stable and unstable isotopic composition by mass spectrometry. Independently, the optical identification of opaque minerals has been brought to an advanced state. All these developments have opened the way for progress in the understanding of the paragenesis and genesis of minerals, subjects to which experimentation at high temperatures and pressure now contribute materially; and for practical applications in many fields, including ore deposits, beneficiation, ceramics, refractories, cement, sinters, and fuels.

Luetheite was found at a small prospect in Santa Cruz County, Arizona, as crystals in vugs in rhyolite porphyry. A few specimens were found on the dump, none seen in place. Occurs in silicified porphyry (quartzsericite-alunite) with chenevixite and hematite. Crystals indian blue inclining to greenish, H = 3, Dmeas = 4·28.

Crystals monoclinic 2/m and tabular on a {100}, also a plane of distinct cleavage; other forms are {110}, {140}, {011}. Space group perhaps P21/m with a = 14·743Å, b = 5·093, c = 5·598, β = 101° 49′; strongest lines are 3·498Å (10), 310, 111; 7·208 (7), 200; 2·507 (5), 120, 510. Feebly pleochroic in pale blue in thin section, γ = β > α. Indices are α = 1·752, β = 1·773, γ = 1·796; 2Vγ = 88° (calc.); dispersion is moderate ν > ρ. α ∥ [010], γ: [001] 10° in obtuse β. Duplicate chemical analyses averaged CuO 28·9%, Al2O3 18·4%, As2O5 40·5%, H2O 9·3% giving 2[Cu2Al2 (AsO4)2(OH)4·H2O].

Named for R. D. Luethe, geologist for Phelps Dodge Corporation. Chenevixite from Las Animas, Sonora, analysed to give Cu2Fe2(AsO4)2(OH)4·H2O. Powder data are close to luetheite, and the cell is monoclinic 2/m, probably P21/m, with a = 15·006A, b = 5·189, c = 5·724, β = 102°15. The measured specific gravity is 4·38, Dcale. = 4·59. Crystals tabular on a {100} with a habit very similar to luetheite. Indices are α = 1·92 , β = 1·96, γ = 2·04, 2Vγcale. = 75°; α ∥ [100], γ nearly ∥ [001].

Archerite, (K, NH4)H2PO4, a new mineral, has been found in Petrogale Cave, 36 km east of Madura Motel (31° 54′S, 127°00′E) Western Australia. Archerite and biphosphammite together with aphthitalite, halite, syngenite, stercorite, oxammite, weddellite, whitlockite, guanine, newberyite, calcite, (NH4)2Ca(HPO4)2·H2O, and an unknown occur as stalactites and wall and floor crusts.

Archerite is tetragonal with second order prisms and pyramids in crystals up to 2 mm in length with D 2·23, ω 1·513, ε 1·470, all close to artificial KH2PO4. The mineral is soft, has a white streak, and is soluble in cold H2O. Cell dimensions of natural archerite were not determined and the composition was calculated from measurements of selected powder lines correlated with charts prepared from end-member data and by chemistry which gave 81% KH2PO4 and K2O 10·8, NH2 3·46 respectively, the latter corresponding to (K0·74(NH4)0·26)H2PO4.

The name is for Dr. M. Archer, Curator of Mammals, Queensland Museum. Type material is stored in the collections of the Government Chemical Laboratories, Perth, Western Australia.

Nickelblödite, the nickel analogue of blödite, has been discovered in nickel mines at Kambalda and Carr Boyd Rocks in Western Australia. The Kambalda sample, found in an underground opening, has a composition corresponding to Na2·02(Ni0·79Mg0·14Fc0·05)(SO4)2·00·3·17H2O. The sample from Carr Boyd Rocks, collected from an open pit, is a more magnesian variety, with a composition corresponding to Na1·93 (Ni0·55Mg0·46Cu0·02Co0·02)(SO4)2·01·4·39H2O. The mineral occurs as a surface efflorescence on nickel-rich sulphide ore in both cases. Nickelblödite is light green and transparent, and occurs as tabular crystallites up to 150 μm in diameter. The Kambalda material is biaxially negative with 2V = 60–70° α = 1·513, β(calc) = 1·518 and γ = 1·520. D 2·43, indentation hardness VHN 139. The Carr Boyd material has lower refractive indices and hardness. Strongest lines of the indexed powder pattern (Kambalda sample) are 4·466(9), 4·193(7), 3·720(6), 3·223(10), 3·190(8), 2·589(6). These measurements conform to a monoclinic unit cell with α = 10·87, b = 8·07, c = 5·46Å, and β = 100·72°. The possibility of H3O+ substitution is discussed.

Three-dimensional counter-diffractometer data and a full-matrix least-squares method have been used to refine the crystal structure of a sub-silicic hastingsite in the space group C2/m. The chemical composition of the amphibole is with ceil parameters a = 9·8659(4), b = 18·0139(8), c = 5·3545(2)Å, and β = 105·082(1)°. Unit weights were used throughout the refinement and the final R-factor for 1263 observed non-equivalent reflections was 4.1%. The mean tetrahcdral bond length for aluminous amphiboles varies linearly with the total amount of tetrahedral A1. Curves are derived relating individual mean bond lengths with A1 occupancy. The positional disorder on the A-site of the aluminous amphiboles appears to be partly related to the amount of substitution of A1 into the T(2) tetrahedron.

New X-ray powderdata are presented for vandendriesscheite, fourmarierite, masuyite, and wölsendorfite. Literature data on the known U-Pb hydrated oxides is reviewed, and suitable criteria for their distinction are set forth.

An unusual tennantite, containing 4·64% Pb, has been found on a mineral specimen from Sark's Hope Mine collected in 1843. An electron-probe analysis is given, together with visible spectrum reflectance data, quantitative colour values, VHN, and cell dimensions determined from X-ray powder diffraction photographs.

Ktenasite from Glomsrudkollen zinc mine, Modum, Norway, is menoclinic, space group P21/c. The cell dimensions are a 5·598, b 6·121, c 23·762Å, β 95·55° The chemical formula is (Cu3·5Zn1·5)(SO4)2 (OH)6·6H2O with Z = 2; ρcale 2·96 g/cm3, ρobs 2·94 g/cm3. The mineral is biaxial negative with α (colourless) 1·574, β (bluish green) 1·615, γ (light green) 1·628, 2Vα 59°.

During the summer of 1967 willcmite was found for the first time in the Ilímaussaq alkaline intrusion, South Greenland. The willemite occurs in an albitite together with aegirine/acmite, albite, analcime, arfvedsonite, apatite, chkalovite, hemimorphite, microcline, monazite, natrolite, naujakasite, neptunite, sphalerite, and polylithionite. Analytical, optical, and X-ray data were obtained from the willemite. Willemite from a calcite vein at Franklin Furnace, New Jersey, and from a quartz vein at Mussartût, South Greenland, were also examined.

One of the willemite crystals from Ilimaussaq was a trilling on <100>. This is the first time willemite has been found as a trilling.

Microprobe and X-ray investigation of a mineral occurring with breithauptite, nickeline, and other arsenides in the naujaite at Igdlúnguaq, Ilímaussaq alkaline massif, S. Greenland, shows that this mineral, which was formerly misidentified as ‘maucherite’, is a westerveldite (Fe0·85Ni0·15)As, of much iron-richer composition than the nickeloan westerveldites from the only two other known occurrences of this mineral. Westerveldite from Igdlúnguaq was presumably formed by reaction of nickeline with iron-rich solutions under conditions of reheating at temperatures of about 450° C and under partial pressures of arsenic below those necessary to stabilize nickeline. Sulphur-bearing löllingite occurs as exsolution blades in the westerveldite. Iron-rich nickeline, up to a composition (Ni0·82Fe0·18)As0·95Sb0·05, was presumably formed by recrystallization of nickeline in the transition stage just before this mineral became unstable and was replaced by westerveldite.

The second occurrence of pyrobelonite, MnPb(VO4)(OH), first recorded at långban, Sweden, is reported. It was found with other manganese and iron minerals at the site of an abandoned 19th-century manganese mine at Tŷ Coch near South Cornelly, Mid Glamorgan, Wales. Reflectance values for pyrobelonite from Tŷ Coch, topotype material from Långban, and for two of the minerals associated with pyrobelonite at Tŷ Coch, vanadinite and hausmannite, are given. Electron-probe analyses of pyrobelonite from both localities give results that are in good agreement with its theoretical composition but disagree with the only previous published analysis.

Phosphate minerals are widespread minor constituents of the pallasites. Both anhydrous primary and hydrous decomposition/alteration phosphates occur. The primary minerals, in decreasing order of abundance, are whitlockite, stanfieldite, and farringtonite, as well as a possibly new phosphate. The decomposition phosphates are compositionally heterogeneous and thus complex. Some may be new minerals. The phosphate minerals serve as the major repository for the alkali elements in pallasites, with individual crystals containing up to several percent of Na+K. Equilibrium established between coexisting phosphide and phosphate defines a relatively narrow range of ƒO2 values.

The formation of ilmenite from titanomagnetite frequently shows separate generations of production. The ilmenite products can be combined with the magnetite host to represent the intermediate stages in this development. Use of the Buddington and Lindsley (1964) geothermometer in conjunction with this method provides a number of points in the temperature and oxygen-fugacity history of a single, complex magnetiteilmenite grain.

Application of the method is illustrated by an example from the Freetown layered gabbro. A titanomagnetite exsolved granular ilmenite whilst cooling and this process ceased at 930° and an oxygen fugacity of log ƒO2 = −11·5. Further cooling and exsolution continued until the grain reached 662 °C and log ƒO2 = −19·0, producing distinct ilmenite lamellae.

Chemical, X-ray, and optical analyses of eight Ca-rich pyroxenes and three coexisting Ca-poor pyroxenes from the gabbros of the Marangudzi ring complex, Rhodesia, are presented. Both the series show limited Fe-enrichment. High Ca-content of the clinopyroxenes together with their restricted Fe-enrichment, having a trend from Ca44·8Mg42·6Fe12·6to Ca42·7Mg37·7Fe19·6, could be indicative of an alkaline nature. But the presence of a Ca-poor pyroxene phase with a compositional trend between Ca2·9Mg71·2Fe25·9 and Ca3·1Mg63·0 Fe34·9 onwards in small amounts suggests tholeiitic to calc-alkaline nature. Certain characteristics in the variation in composition of the pyroxenes confirm a transitional nature of the Marangudzi parent magma, originating at a depth comparatively greater than the normal tholeiitic magma, but less deep than alkaline magma, at a fairly high pressure. The Marangudzi pyroxenes are compared with the pyroxenes of the similar world-wide igneous complexes.

The Bondoc Peninsula meteorite appears to be unstable and is disintegrating as the result of terrestrial corrosion. The meteorite is complex with occasional 1 to 3 cm dia. ‘Nodules’ of ‘iron-class’ material, fig. 1, within which are numerous non-metallic inclusions. These range in size from 0·5–1·5 mm and vary in shape from the extremes of angular to globular, shown in figs. 2 and 3. The metallic groundmass of fig. 1 is a polycrystalline array of kamacite grains that are equant in shape and about 3 to 4 mm dia. The boundaries between these kamacite grains are heavily invaded by corrosion product. The films of cracked schreibersite and strips of compositionally zoned taenite that are present at the kamacite boundaries each contribute about 2 % by volume and their average Ni contents are about 45 wt% and 40 wt% respectively. When these figures are combined with the average 6·2 wt% Ni, 0·75 wt% Co, and 0·02 wt% P of the kamacite the resulting bulk composition of the metal is ∼ 7·5 wt% Ni, ∼ 0·7 wt% Co, ∼ 0·3 wt% P. Nital etching reveals partially annealed Neumann bands in the kamacite, indicating a late stage reheating below about 500°C. However, the M profile method of Wood (1967) when applied to the zoned taenite yields a cooling rate of 0·1–0·5°C/Myr before this reheating event.

The angular inclusions are relatively coarsely crystalline and commonly have massive chromite and tridymite crystals, with pyroxene, anorthite, and whitlockite usually present. Most angular inclusions also contain small particles of metal (10–40 µm dia.) interstitial to the mineral phases in the depth of the inclusion. Small quantities of sulphide and phosphide are similarly located. The metal in the angular inclusions is not detectably zoned and both kamacite and taenite show a range of Ni contents that vary with particle size in the manner previously observed by Powell (1969) for a range of conventional mesosiderites. We have in addition measured the Co and P contents of this metal and find P < 0·1 wt% and the Ni and Co analyses are consistent with equilibration in the ternary Fe-Ni-Co equilibrium diagram at ∼ 450 °C.