Okhotskite, an Mn3+-dominant pumpellyite-group mineral, is monoclinic, A2/m, a = 8.887, b = 6.000, c = 19.55 Å, β = 97.08°, Z = 1. The formula is

(Ca7.63Na0.17K0.01)Σ7.81(Mn2.752+Mg1.10)Σ3.85(Mn4.503+Al1.87Fe1.613+Ti0.02)Σ8.00Si12.13O39.71(OH)16.29,

which simplifies to Ca8(Mn2+,Mg)4(Mn3+,Al,Fe3+)8Si12O5∂-n(OH)n. Strong lines in the X-ray powder diffraction pattern are: 4.76(60)(004, 111), 3.87(70)(202), 2.96(100)(115, 300), 2.88(25)(022), 2.72(70)(302), 2.67(45)(3̄04, 3̄11), 2.55(45)(024, 3̄13) and 2.38(45)(304).

Its colour is deep orange with a pale orange streak and vitreous lustre. Transparent. Non-fluorescent. H6 (Mohs). Density (calc.) = 3.40 g/cm3. Optically biaxial negative, 2V(meas) = 46(5)°, 2V(calc) = 46°, dispersion indiscernible. Refractive indices: α = 1.782(5), β = 1.820(5), γ = 1.827(5). Orientation: Y = b, c∧Z = 9–14° in acute angle of β. Pleochroism is distinct: X yellow, Y and Z deep orange. Absorption: X < Y < Z.

This mineral occurs as fine prisms up to 0.2 mm long and forms aggregates in network veinlets cutting hematite ore from the Kokuriki mine in the Tokoro district, eastern Hokkaido, Japan. Associated minerals are: hematite, piemontite, quartz, neotocite, bementite, apatite, Mn-oxides, inesite and rhodochrosite. The mineral is named okhotskite for the Sea of Okhotsk, along which the mine is located.

Camptonites from the Taourirt region of Morocco contain kaersutite crystals that exhibit clear sector zoning. The electron microprobe reveals systematic variations between sectors, with preferential enrichment of Mg and Si in sector (011) and higher values for Fe, Ti and Al in sectors (110) or (100). These differences are similar to those recorded in clinopyroxenes with hour-glass zoning where this type of crystallization has been known for more than a century.

We use an approach based upon the atomistic or Born model of solids, in which potential functions represent the interactions between atoms in a structure, to calculate the infrared and Raman vibrational frequencies of forsterite. We investigate a variety of interatomic potentials, and find that although all the potentials used reproduce the structural and elastic behaviour of forsterite, only one potential (THB1) accurately predicts its lattice dynamics. This potential includes ‘bond-bending’ terms, that model the directionality of the Si-O bond, which we suggest plays a major role in determining the structural and physical properties of silicates. The potential was derived empirically from the structural and physical data of simple oxides, and its ability to model the lattice dynamics of forsterite is a significant advance over previous, force-constant models, which have been simply derived by fitting to the spectroscopic data that they aim to model. The success that we have had in predicting the lattice dynamics of forsterite indicates that the potential provides the previously elusive yet fundamental, quantitative link between the microscopic or atomistic behaviour of a mineral and its macroscopic or bulk thermodynamic properties.

Yugawaralites from two localities in Japan consist of growth sectors with variable 2V values and extinction angles. The optical variations cannot be explained on chemical grounds because the mineral shows very little chemical variation but they can be explained on the basis of Al/Si ordering. The v{021} sectors (Pa setting) are composed of optically triclinic bands, and the k{110} sector consists of both triclinic bands and monoclinic homogeneous domains. An electrostatic charge of the Al/Si ordered structure is balanced along a two-dimensional atomic arrangement exposed on the side face of a growth step. If the Si tetrahedron is produced after the calcium ion, the Si ion will be replaced during growth by an Al ion due to the local effect of the calcium ions. When a side plane of growth steps of yugawaralite is not normal to the (010) glide plane, a symmetrical equivalence of two Si sites with respect to the Ca ion will be lost at the surface, and as a consequence ordering will occur and the symmetry of crystal will be reduced. The monoclinic, homogeneous sector might be produced on the very finely kinked surface. The space group of the triclinic sector will be P1, while that of the monoclinic sector will be Pc.

Four grains of zirconolite and baddeleyite have been found in two plagioclase-rich adcumulates from the Laouni layered intrusion (Southern Hoggar, Algeria). Zirconolite is poor in REE; baddeleyite is chemically close to ZrO2 and contains minor amounts of Hf. They are considered to be crystallization products of pockets of intercumulus liquid. The preferential distribution of zirconolite in anorthosite is explained in terms of expulsion of the intercumulus liquid by sintering or annealing of plagioclase. The crystallization of baddeleyite reflects the sharp increase of Zr in the trapped intercumulus liquid.