Heat Capacities of Natural Antlerite and Brochantite at Low Temperature

The investigation of a magnetic component of the heat capacity of natural samples of copper sulfates antlerite Cu₃SO₄(OH)₄ in the temperature range below 40 K and brochantite Cu₄SO₄(OH)₆ below 55 K has been carried out. A regular component of the heat capacity has been calculated from experimental data of adiabatic calorimetry. In the low-temperature area of (0 to 55) K two peaks of magnetic heat capacity for brochantite have been registered. The contributions of anomalous component Δ<i>S</i>_tr into entropy of the minerals are (11 ± 3) J·mol^–1·K^–1 for antlerite and (5.3 ± 1.5) J·mol^–1·K^–1 for brochantite