The variation with temperature of the thermal con­ductivity and the X-ray structure of some micas I—The thermal conductivity up to 600° C

The authors recently had occasion to measure the thermal conductivities of several varieties of mica up to a temperature of 600° C. In the course of this work it has been observed that whereas the thermal conductivities of the muscovite varieties of mica alter but little over this temperature range, the thermal conductivities of certain phlogopite micas decrease to about one-third of their initial values when the micas are heated to about 200° C. In such cases there is incomplete reversibility in the thermal conductivity temperature curve on cooling. Subsequent examination of these micas by means of X-ray crystal analysis has revealed the fact that in those samples which suffered appre­ciable change in conductivity, the arrangement of the elementary crystals composing the mica laminae becomes displaced from their ordered setting at approximately the same temperature as the thermal conductivity change. The present paper describes the thermal conductivity experiments, which are believed to be the first determinations carried out on mica to high temperatures. In the paper which follows, Mr. W. A. Wood describes the X-ray experiments on some of these samples of mica.