Laboratory duplication of textures previously known only from naturally occurring ooids was accomplished for the first time on heated and experimentally compacted ooids (250 °C, 364 kg/cm2). Crystals of neomorphic calcite developed, replacing aragonitic ooids. In places the original fabric survived. Preservation of concentric laminae in ooids during this process indicates absence of an intervening stage of void formation. This polymorphic transformation is a wet process and temperature dependent.