Lattice thermal diffusivities of eleven orientated natural and synthetic quartz samples were measured using a laser-flash apparatus (LFA). For α-quartz, thermal diffusivity (D) decreases with temperature, so that directionally averaged values of D(T) between 20° and 500°C can be fit with D(T) = 1/(0.0017T + A), where A varies from 0.12 to 0.18 among the samples and D is in mm2/s. For β-quartz, D decreases very slightly or is constant with temperature. Values of D measured along [001] exceed those measured along [100] at all temperatures studied. A sharp decrease of D(T) marks the α-β phase transition, consistent with correlation of 1/D with C P in the damped harmonic oscillator model. Due to the rapidity of the laser-pulse and the dynamic nature of the measurements, the raw data show evidence of latent heat being released at the transition temperature over ∼50 ms. D(T) values within 10 K of the transition are affected both by latent heat release and by the phase change. For our suite of samples, D at all temperatures varies by ±7% from the overall average. This range is outside the 2% experimental uncertainty. To ascertain causes of D variations, we characterized out samples using infrared absorption spectroscopy, electron microprobe analyses and secondary ion mass spectrometry. Differences between the samples seem to result from the interplay of different impurity types: cations that replace Si in the silicate tetrahedra, cations squeezing into the lattice, and OH. Although limitations in quantifying amounts of trace impurities and poor understanding of where impurities reside in the lattice hamper interpretation, it seems that samples containing more substitutional impurities (e.g., Al3+) have higher diffusivities along [001], those with more interstitial defects (e.g., Li+) have higher diffusivities along [100], and that OH reduces D.