X-ray diffraction refinement of the crystal structure of eosphorite has been carried out with reference to the orthorhombic space group Cmca. The structure is similar to that previously described by Hanson (1960), but the standard deviations are improved. Optical absorption and photoluminescence have also been studied for this mineral. Two sharp emission lines, denoted as R1 and R2, superimposed to a broad band (630-750 nm) have been related to the presence of Cr3+ ions. The excitation spectrum of these emissions confirms that the absorption (excitation) bands centred at 431 nm and 585 are related to with 4A2 → 4T1 and 4A2 → 4T2 spin allowed transitions of this ion.

Caryinite from Långban, Sweden is associated with barite, richterite, manganberzeliite, hedyphane, sarkinite or eveite, and an exsolved fermorite-like mineral. The crystal structure of caryinite, space group I2/a, a 6.855(2), b 13.147(3), c 11.479 (4) Å, β 98.97°, V 1022.0(5) Å3, has been refined to a conventional R = 3.5% using 1295 observed [F > 3α(F)] reflections. Caryinite is isostructural with alluaudite and shows the following key features: (1) Pb is ordered at X2, Mg is ordered at M2, Mn is disordered over M1 and M2, Ca is disordered over M1 and X1 and Na is disordered over X1 and X2, and (2) the X1 and 02 atoms of the X1 polyhedron show positional disorder. With the above site preferences taken into consideration, the assignment rules of Moore and Ito (1979) can now be used to accurately predict site occupancies for caryinites and arseniopleites using chemical data only. On the basis of the general structural formula X2X1M1M22[AsO4]3 (Z = 4), caryinite is (Na, Pb) (Ca, Na) Ca (Mn, Mg)2 [ASO4]3; the analogous formula for arseniopleite is Na(Ca,Na)Mn(Mn,Mg)2[AsO4]3. Carinite has Ca dominant at M1; by analogy, arseniopleite should have Mn dominant at M1.

The structure of chrysotile, an important asbestos mineral, consists of layers curled concentrically or spirally into tubes. Published transmission electron microscope (TEM) images suggest that successive layers are generally stacked out of register with one another. However, a lattice model can be constructed in such a way that each layer can be stacked in register with the next, five times around the circumference, so that the structure exhibits a global 5-fold symmetry. We report here TEM observations confirming that chrysotile asbestos can form crystals with this structure, the first observation of five-fold symmetry in a natural crystalline material.

Interpretation of grain size measurements in terms of the kinetics of grain growth depends on the ability to define the temperature variation of mineral growth rates. An outline is presented of the application to mineral growth rates of a corresponding states equation (CSE), which provides a relationship of growth rate to a reduced temperature function. Additionally, growth rates exhibit a 'compensation effect' between the pre-exponential constant and the activation energy in the standard Arrhenius equation, analogous to that shown by diffusion data. The general systematics of activation energy, equilibrium temperature and growth rate maxima are controlled by the relationships of the CSE, the standard Arrhenius equation and the compensation effect, and on this basis the temperature variation of growth rate between the equilibrium and the glass temperature may he estimated.