A new miniature gasketed diamond anvil high pressure cell has been constructed to perform optical and x-ray diffraction studies on single crystals under hydrostatic pressure. For x-ray studies the cell is mounted on a standard goniometer head which may be attached to either a standard precession camera or single crystal orienter taking advantage of counting methods. The pressure cell has been used successfully in the study of the two high pressure phases of calcium carbonate, CaCO3(II) and CaCO3(III).

A critical review of experimental technique for measuring high pressures has been made. The broad coverage includes discussions relating to (a) the establishment of a primary pressure scale using the free-piston gage, (b) the selection and precise measurement of identifiable phase changes as fixed pressure points, and (c) the use of interpolation and extrapolation techniques such as resistance gages, equations of state, and optical changes. The emphasis is on static pressure measurements above 10 kbar, but shock measurements are also considered for completeness. The pressure values to be associated with the fixed points have been analyzed in detail. Temperature measurement in the high pressure environment is also reviewed. The accuracy with which pressures can be measured has been carefully considered; the maximum accuracies now obtainable are considered to be of the order of 0.02 percent at 8 kbar, 0.25 percent at 25 kbar, 2 percent at 50 kbar, and 4 percent at 100 kbar.

The results of the published work on the high pressure-high temperature properties of the AB-type compounds have been compiled and evaluated. All pressure studies above the range of 1 kilobar have been included with an. emphasis on the accurate charterization of the solid-solid. phase' boundaries and the experimental melting curves. Whenever x-ray diffraction data are available for the high pressure phases, they have also been reviewed. Phase diagrams are included for all compounds in which measurement of more than one point along the phase boundary was made. This review discusses a total of 87 comp01,lnds and 212 distinct high pressurehigh temperature phases.

The effect of pressure on the lattice parameter of magnetite has been determined at room temperature up to 320 kbar by means of X ray diffraction employing a diamond anvil high‐pressure cell. By using the Birch‐Murnaghan equation with a (∂KT/∂P)T∣P=0 value of 4 ± 0.4 the isothermal bulk modulus at zero pressure was calculated to be 1.83 ± 0.10 Mbar. The X ray diffraction study also revealed that at pressures greater than 250 kbar, magnetite transforms to a high‐pressure phase, which reverts to magnetite at pressures below 50 kbar. It is possible to index this high‐pressure phase as being monoclinic. If it is assumed that the unit cell contains two molecules, the density is in agreement with the density predicted for a phase of Fe3O4 having all of the iron atoms in sixfold coordination.