Four polymorphs of Zn(OH)2 have now been recorded from an oxidised vein exposure near Milltown, Ashover, Derbyshire; sweetite, wülfingite, γ-Zn(OH)2, and ashoverite. The last is a new mineral, a tetragonal modification of Zn(OH)2 containing minor quantities of Pb, Cd and Ca. Its unit cell dimensions are a 6.825(2) and c 33.36(4) Å, giving V = 1554 Å3; Z = 32; space group I41/amd, I41md, or I4¯2d; Dmeas. 3.3, Dcalc 3.44 g cm−3. Ashoverite occurs as colourless platy crystals associated with fluorite; it is uniaxial positive with ω 1.629(2), ε 1.639(2). The chemical composition of sweetite is compared with that of ashoverite.

Synthetic Eu-anorthite of the alkali feldspar structure type has been refined to Rw = 4.7% using 3-D counter diffractometer data and full-matrix least-squares methods. The chemical composition of the feldspar is Eu0.92Al1.76Si2.24O8, based on both occupancy refinement of the Eu atom site and estimation of the Al/Si distribution calculated from the mean T-O bond length. The unit cell parameters are a = 8.373(1), b = 12.959(1), c = 7.124(1) Å, and β = 115.51(1)° and the symmetry is enhanced to C2/m. Mean bond lengths are T(1)-O = 1.677 Å, T(2)-O = 1.668 Å, and Eu-O = 2.721 Å. The average Al/Si distribution over the T(1) and T(2) sites calculated from the mean T-O bond length is in fairly good agreement with an estimate of the Al content from the bond strength calculation; the Al partition is calculated as t1 = 0.47 and t2 = 0.41 respectively. Summing the bond strengths of these Eu and partially disordered Al/Si cations approximates to electrostatic neutrality for the anion content of the feldspar structure, indicating that this synthetic Eu feldspar can be non-stoichiometric, signifying vacancies on the alkali cation site.

Plagioclase and melilite generally show a positive Eu anomaly. A fair insight into the driving force of this anomaly can be afforded by the crystallo-chemical affinities of Eu2+ and Eu3+ cations to the crystal structures of their host minerals; (1) ioinic radius, (2) electrostatic charge balance and (3) tolerance for non-stoichiometry of the crystal structure.

This is the final report on the nomenclature of pyroxenes by the Subcommittee on Pyroxenes established by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. The recommendations of the Subcommittee as put forward in this report have been formally accepted by the Commission. Accepted and widely used names have been chemically defined, by combining new and conventional methods, to agree as far as possible with the consensus of present use. Twenty names are formally accepted, among which thirteen are used to represent the end-members of definite chemical compositions. In common binary solid-solution series, species names are given to the two end-members by the ‘50% rule’. Adjectival modifiers for pyroxene mineral names are defined to indicate unusual amounts of chemical constituents. This report includes a list of 105 previously used pyroxene names that have been formally discarded by the Commission.