Thermal behavior of two new exhalation copper-bearing minerals, bradaczekite and urusovite, from the Great Tolbachik Fissure Eruption (1975-1976, Kamchatka Peninsula, Russia) has been studied by X-ray thermal analysis within the range 20-700°C in air. The following major values of the thermal expansion tensor have been calculated for urusovite: α₁₁ = 10, α₂₂ = α_b = 7, α₃₃ = 4, α_V = 21 × 10^-6°C^-1, μ = c^α₃₃ = 49° and bradaczekite: α_11aver = 23, α₂₂ = 8, α_33aver = 6 × 10^-6°C^-1, μ(c^α₃₃) = 73°. The sharp anisotropy of thermal deformations of these minerals, absences of phase transitions, and stability of the minerals in the selected temperature range corresponding to conditions of their formation and alteration during the posteruption period of the volcanic activity are established.