VOLUME BEHAVIOR OF HYDROUS MINERALS AT HIGH-PRESSURE AND TEMPERATURE .1. THERMAL-EXPANSION OF LAWSONITE, ZOISITE, CLINOZOISITE, AND DIASPORE

The temperature dependence of the lattice parameters of synthetic laws onite [CaAl2Si2O7 (OH)(2) . H2O], natural zoisite [Ca2Al3Si3O12 (OH)], natural clinozoisite [Ca2Al3Si3O12 (OH)], and synthetic diaspore [AlO (OH)] have been measured at ambient pressure. The volume thermal expan sion coefficients for lawsonite, zoisite, and clinozoisite are approxi mately constant over the measured temperature ranges (25-590 degrees C for lawsonite, 25-750 degrees C for zoisite, and 25-900 degrees C for clinozoisite), whereas the thermal expansion of diaspore increases sl ightly over the range 25-300 degrees C. Interestingly, the room-temper ature volume of clinozoisite is greater than that of zoisite, but this situation is reversed above similar to 300 degrees C. The experimenta l results may be summarized as follows: lawsonite: V/V-0 = 1 + 3.16 (/-0.05) x 10(-5) (T - 298), V-0 = 101.51 (+/-0.01) cm(3)/mol; zoisite: V/V-0 = 1 + 3.86 (+/-0.05) x 10(-5) (T - 298), V-0= 136.10 (+/-0.02) cm(3)/mol; clinozoisite: V/V-0 = 1 + 2.94 (+/-0.05) x 10(-5) (T - 298) , V-0= 136.42 (+/-0.05) cm(3)/mol; diaspore: V/V-0 = 1 + 7.96 (+/-0.28 ) x 10(-5) [T - 298 - 20 (root T - root 298)], V-0 = 17.74 (+/-0.01) c m(3)/mol.