Gypsum crystals were grown at 25, 35, and 45 °C from solutions containing different ionic impurities (Mg2+, Na+, Cd2+). Curved gypsum crystals formed from the solutions enriched in magnesium or cadmium, whereas, in the presence of sodium, gypsum always grew undeformed. The mechanism of the curvature is described and an interpretation based on crystallographic considerations is given. Curvature is the result of impurity incorporation followed by crack formation and mechanical twinning which releases the internal stresses.
