Volume behavior of hydrous minerals at high pressure and temperature: I. Thermal expansion of lawsonite, zoisite, clinozoisite, and diaspore

The temperature dependence of the lattice parameters of synthetic lawsonite [Ca-Al₂Si₂O₇(OH)₂·H ₂O], natural zoisite [Ca₂Al₃Si₃O₁₂(OH)], natural clinozoisite [Ca₂Al₃Si₃O₁₂(OH)], and synthetic diaspore [AlO(OH)] have been measured at ambient pressure. The volume thermal expansion coefficients for lawsonite, zoisite, and clinozoisite are approximately constant over the measured temperature ranges (25-590°C for lawsonite, 25-750°C for zoisite, and 25-900°C for clinozoisite), whereas the thermal expansion of diaspore increases slightly over the range 25-300°C. Interestingly, the room-temperature volume of clinozoisite is greater than that of zoisite, but this situation is reversed above ∼300°C. The experimental results may be summarized as follows: lawsonite: V/V₀ = 1 + 3.16 (±0.05) × 10^-5 (T - 298), V₀ = 101.51 (±0.01) cm³/mol; zoisite: V/V₀ = 1 + 3.86 (±0.05) × 10^-5 (T - 298), V₀ = 136.10 (±0.02) cm³/mol; clinozoisite: V/V₀ = 1 + 2.94 (±0.05) × 10^-5 (T - 298), V₀ = 136.42 (±0.05) cm³/mol; diaspore: V/V₀ = 1 + 7.96 (±0.28) × 10^-5 [T - 298 - 20 (√T - √298)], V₀ = 17.74 (±0.01) cm³/mol.