Kinetics of crystal growth from silicate melts: Anorthite and diopside

Rates of linear crystal growth have been measured for diopside and anorthite growing from their own melts by using a microscope heating stage. Rates were obtained for undercoolings of as little as 13°C. The rates are higher for diopside than for anorthite. Maximum growth rates observed are 1.5×10−2 cm/s (ΔT = 194°C) for anorthite and 2.2×10−2 cm/s (ΔT = 105°C) for diopside. For diopside this probably does not represent the maximum rate. Both phases grow with a faceted morphology. Plots of Yη/ΔT versus ΔT indicate that anorthite grows by a surface nucleation mechanism, while diopside grows by a screw dislocation mechanism. These plots can also be used to calculate growth rates at undercoolings less than those at which data have been obtained.