High-temperature X-ray diffractometry was used to study linarite found in association with tenorite, atacamite, chrysocolla, and anglesite in the remnants of an old fumarolic field on Gora-1004 Volcano in the Tolbachik Valley, the last eruptions at which had occurred 1500-2000 B.P. The mineral was found to remain stable until 265±15°C, at which it was dehydrated to produce chalcokyanite, anglesite, and tenorite. The mineral showed a marked anisotropic character of thermal deformation, consistent with its crystal structure. Its thermal strain tensor axes correlate with its optic indicatrix. Its thermal expansion is most active in the direction perpendicular to the plane of CuO₄ chains, the direction followed by the shorter N(p) axis, the N(m) axis coinciding with the direction of the least thermal expansion and the N(g) axis with the highest density trend (along b-axis chains).