Thermal conductivity of short sequences of rock

Numerical models of igneous rock samples provide estimates of the variation in conductivity of discs cut from lengths of core. Ten discs cut from a piece of core have a root mean squared deviation of up to 6 %, depending on quartz content and crystal size. Greater crystal size increases the apparent conductivity of a disc by up to 3.2 % when quartz content is 49 %, but less when quartz content is 30 % or less. Measured conductivity depends on the thickness of the measured disc. When quartz content is low, this difference is well within the normal limits of experimental error, but when quartz content is high, the apparent conductivity will be within the normal limits of experimental error only when the disc is at least 8 mm thick. The estimation of contact resistance between the sample and the bar by using sets of discs of different thickness is unreliable because of variation in mineral content between contiguous discs. Better representation of the conductivity profile is obtained by measuring single discs with an estimation of the contact resistance.