Under near-equilibrium growth or melt conditions, ice crystals in the melt are bounded by two parallel facets (basal planes or c-facets) and rounded surfaces between the facets. We observed such disk-shaped ice crystals perpendicularly to the c-axis in two and three dimensions, and found that the growth and melt shapes are asymmetric. On imposition of a small driving force, a rounded crystal grew to be partially faceted with a loss of vicinal surfaces and a formation of surface-slope discontinuities at the facet edges, and then the partially faceted crystal melted to be rounded with enlarging vicinal surfaces. The rounded surfaces grew with a decreasing curvature and melted with an increasing curvature. (c) 2010 Elsevier B.V. All rights reserved.