A high-temperature X-ray study of the equilibrium forms of albite

s u M M A R V. Complete lattice parameters have been determined ata series of temperatures upto 95o ~ using a furnace on a powder diffractometer for six synthetic supposed equilibrium albites, a non-equilibrium albite, two natural albites, and a heat-treated natural albite. The supposed equilibrium albites were prepared hydrothermally b MacKenzie 0957) for long periods of time and reached or nearly reached a state of no further change at their temperatures of synthesis between 5oo and I ooo ~ A crystal of natural albite and three crystals of heat-treated natural albite were studied by high-temperature, single-crystal methods on a Buerger precession camera up to Iooo ~ for comparison. The lattice angles for each albite decrease smoothly with increasing temperature; the a-axis and the volume increase smoothly with increasing temperature. The rates of change increase with increasing temperature. The c and in some cases the b-axes appear to decrease initially in the range 25-3oo ~ and then subsequently increase. The thermal dilatation is highly anisotropic--the change in a is about twice that in b and about six times that in c over the whole range 25-85o ~ The effect of a tem-perature rise on the lattice parameters of the albites is very similar to the effect of the substitution of potassium on the room-temperature parameters. Plots of c~ * against ~, * for each albite at a sequence of temperatures upto 95o ~ fall on nearly straigh