The Australian SKA Pathfinder (ASKAP) offers powerful new capabilities for studying the polarised and magnetised Universe at radio wavelengths. In this paper, we introduce the Polarisation Sky Survey of the Universe’s Magnetism (POSSUM), a groundbreaking survey with three primary objectives: (1) to create a comprehensive Faraday rotation measure (RM) grid of up to one million compact extragalactic sources across the southern $\sim50$% of the sky (20,630 deg$^2$); (2) to map the intrinsic polarisation and RM properties of a wide range of discrete extragalactic and Galactic objects over the same area; and (3) to contribute interferometric data with excellent surface brightness sensitivity, which can be combined with single-dish data to study the diffuse Galactic interstellar medium. Observations for the full POSSUM survey commenced in May 2023 and are expected to conclude by mid-2028. POSSUM will achieve an RM grid density of around 30–50 RMs per square degree with a median measurement uncertainty of $\sim$1 rad m$^{-2}$. The survey operates primarily over a frequency range of 800–1088 MHz, with an angular resolution of 20” and a typical RMS sensitivity in Stokes Q or U of 18 $\mu$Jy beam$^{-1}$. Additionally, the survey will be supplemented by similar observations covering 1296–1440 MHz over 38% of the sky. POSSUM will enable the discovery and detailed investigation of magnetised phenomena in a wide range of cosmic environments, including the intergalactic medium and cosmic web, galaxy clusters and groups, active galactic nuclei and radio galaxies, the Magellanic System and other nearby galaxies, galaxy halos and the circumgalactic medium, and the magnetic structure of the Milky Way across a very wide range of scales, as well as the interplay between these components. This paper reviews the current science case developed by the POSSUM Collaboration and provides an overview of POSSUM’s observations, data processing, outputs, and its complementarity with other radio and multi-wavelength surveys, including future work with the SKA.

We present an overview of the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey, a Large Program on the European Southern Observatory Very Large Telescope. MAGPI is designed to study the physical drivers of galaxy transformation at a lookback time of 3–4 Gyr, during which the dynamical, morphological, and chemical properties of galaxies are predicted to evolve significantly. The survey uses new medium-deep adaptive optics aided Multi-Unit Spectroscopic Explorer (MUSE) observations of fields selected from the Galaxy and Mass Assembly (GAMA) survey, providing a wealth of publicly available ancillary multi-wavelength data. With these data, MAGPI will map the kinematic and chemical properties of stars and ionised gas for a sample of 60 massive (${>}7 \times 10^{10} {\mathrm{M}}_\odot$) central galaxies at $0.25 < z <0.35$ in a representative range of environments (isolated, groups and clusters). The spatial resolution delivered by MUSE with Ground Layer Adaptive Optics ($0.6-0.8$ arcsec FWHM) will facilitate a direct comparison with Integral Field Spectroscopy surveys of the nearby Universe, such as SAMI and MaNGA, and at higher redshifts using adaptive optics, for example, SINS. In addition to the primary (central) galaxy sample, MAGPI will deliver resolved and unresolved spectra for as many as 150 satellite galaxies at $0.25 < z <0.35$, as well as hundreds of emission-line sources at $z < 6$. This paper outlines the science goals, survey design, and observing strategy of MAGPI. We also present a first look at the MAGPI data, and the theoretical framework to which MAGPI data will be compared using the current generation of cosmological hydrodynamical simulations including EAGLE, Magneticum, HORIZON-AGN, and Illustris-TNG. Our results show that cosmological hydrodynamical simulations make discrepant predictions in the spatially resolved properties of galaxies at $z\approx 0.3$. MAGPI observations will place new constraints and allow for tangible improvements in galaxy formation theory.

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.

A specimen from Långban, Sweden, was found to consist largely of sjögrenite in which segregation and ordering of the metal cations had occurred, yielding an intergrowth of regions of two main types with compositions probably of or near Mg2/3Fe1/3(OH)2(CO3)1/6(H2O)0·4 and Mg12/13Fe1/13(OH)2(CO3)1/26(H2O)0·8. To a smaller extent segregation had proceeded further, giving regions probably approximating to the end-member Mg(OH)2.H2O. It is suggested that the names sjögrenite and pyroaurite be used for the 2H- and 3R- polytypes of this structure irrespective of Mg:Fe ratio, segregation, or cation ordering.

The crystal structure of coalingite (Mg10Fe2(OH)24(CO3)·2H2O) has been determined using single-crystal X-ray methods. The mineral is trigonal, with space group Rm, a H = 3·12, c H = 37·4 Å, Z = ½, and (0001) cleavage. The structure is of a layer type, and is based on a structural element about 12·5 Å thick in the c-direction and consisting of two brucite-like layers and one disordered layer containing carbonate ions and water molecules and resembling those in sjögrenite and pyroaurite. The unit cell comprises three of these structural elements stacked together in the c-direction. The Mg2+ and Fe3+ ions are randomly distributed among all the octahedral sites of the brucite-like layers. The structure closely resembles those of sjögrenite and pyroaurite, but has two brucite-like layers between each CO3 2−−H2O layer where these have one. There is a tendency to random interstratification, and the crystals appear to contain intergrown regions of brucite and of sjögrenite or pyroaurite. Coalingite-K probably has a similar structure, but with three brucite-like layers between each -H2O layer; its idealized formula is probably Mg16Fe2(OH)36(CO3).2H2O.

Eleven specimens of natural or synthetic truscottite or gyrolite-truscottite intergrowth were studied by analytical electron microscopy and X-ray powder diffraction. The results suggest that, in absence of substitution, the formula of truscottite is Ca14 (Si24O58)(OH)8 · ∼ 2H2O. Truscottite can accommodate Al and K in absence of each other to the extents of 1.4 atoms of Al or 0.5 atoms of K in the above formula. Substitution of Al causes a small increase in cell dimensions, which can approach those of reyerite, but substitution of K has negligible effect.

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.

Three groups of minerals are discussed, which are typified by pyroaurite and sjögrenitc, hydrocalumite, and ettringite. All show interesting structural features. In the pyroaurite-sjögrenite group, brucite-likc layers carrying a net positive charge alternate with layers in which the oxygen atoms of carbonate groups and water molecules are statistically distributed on a single set of sites; other anions may replace the carbonate, especially in synthetic phases. Hydrocalumite and related synthetic phases also have layer structures in which positively charged main layers alternate with intermediate layers containing anions and water molecules; the anions occur in cavities and their nature can again vary widely. In the ettringite group, the structures are based on positively charged columns, between which occur channels containing anions and sometimes also water molecules. This group includes thaumasite, the only natural mineral known to contain silicon six-coordinated by oxygen that is not a high-pressure phase. The thermal dehydration behaviour in each group is briefly considered.

The crystal structure of kilchoanite, Ca6(SiO4)(Si3O10), has been determined from three- dimensional X-ray methods (r = 0·089 on 348 independent reflections). It is closely related to that of γ-Ca2SiO4, which is olivine-like. In kilchoanite, slabs of γ-Ca2SiO4 structure alternate with ones composed of Ca ions and finite chains of three tetrahedra; these have the composition Si3O10 8− and have rarely been observed previously. A related, synthetic phase, 8CaO. 5SIO2, probably has a similar structure but with a higher proportion of γ-Ca2SiO4 regions, and should thus be formulated as Ca8(SiO4)2(Si3O10). Disordered synthetic phases also occur that appear to have similar structures with still higher proportions of γ-Ca2SiO4 regions. These phases collectively form an interesting contrast to the chondrodite minerals.

The crystal structure of killalaite has been approximately determined, using a crystal from the original locality. The ionic constitution is Ca3+x (H1–2x Si2O7) (OH), with x ≈ 0·2 for the crystal studied. Crystal data are: monoclinic pseudo cell with a 6·807, b 15·459, c 6·811 Å, β 97·76°, space group P21/m, Z = 4, D x-ray = 2·94 gcm-3. Additional, very weak reflections indicate a B-centred monoclinic true cell with doubled a and c. The structure was determined using only the pseudo cell reflections, and includes one fractionally occupied Ca site; the larger true cell possibly arises from ordering of Ca atoms in these sites, together with associated small shifts of other atoms. There are weak indications that the degree of occupancy of this site may be variable. The X-ray powder pattern has been indexed and a calculated pattern is also given. A synthetic compound called ‘Phase F’ by Aitken and Taylor (1960) appears identical with or closely similar to killalaite.

Tobermorite minerals vary in some proper lies, notably in whether or not unidimensional lattice shrinkage occurs by about 300 °C to give a 9·3 form; specimens that do this are called normal, and ones that do not, anomalous. Data are compared for thirteen natural tobermorites and the extent to which normal or anomalous character is related to other properties is examined. The most definite correlations found are with chemical composition and morphology. The conditions of formation of normal and anomalous tobermorites are discussed in the light of synthetic evidence.

Euclid is the next ESA mission devoted to cosmology. It aims at observing most of the extragalactic sky, studying both gravitational lensing and clustering over ~15,000 square degrees. The mission is expected to be launched in year 2020 and to last six years. The sheer amount of data of different kinds, the variety of (un)known systematic effects and the complexity of measures require efforts both in sophisticated simulations and techniques of data analysis. We review the mission main characteristics, some aspects of the the survey and highlight some of the areas of interest to this meeting.

The Dominion Radio Astrophysical Observatory (DRAO) is carrying out a survey as part of an international collaboration to image the northe, at a common resolution, in emission from all major constituents of the interstellar medium; the neutral atomic gas, the molecular gas, the ionised gas, dust and relativistic plasma. For many of these constituents the angular resolution of the images (1 arcmin) will be more than a factor of 10 better than any previous studies. The aim is to produce a publicly-available database of high resolution, high-dynamic range images of the Galaxy for multi-phase studies of the physical states and processes in the interstellar medium. We will sketch the main scientific motivations as well as describe some preliminary results from the Canadian Galactic Plane Survey/Releve Canadien du Plan Galactique (CGPS/RCPG).