Macroscopic thermal dilatation coefficients as well as those of the lattice were precisely measured along the principal crystallographic directions of magnesium single crystals between room temperature and 650C. The vacancy concentration was obtained as a function of temperature and it reached a value of 72 x 10-5 in the neighborhood of the melting point. An appreciable anisotropy in the atom rearrangement appeared during the defect-formation process, which seemed to correspond to the preferential climb of edge dislocations in the prismatic planes. From the behavior of the excess in macroscopic dilatation as a function of temperature, the formation energy was found to be 0.58eV per vacancy, while the formation entropy was practically zero. Vacancy-Formation Energy and Entropy in Magnesium Single Crystals. C.Janot, D.Malléjac, B.George: Physical Review B, 1970, 2[8], 3088-98