What original grain sizes are obliterated so grains become uniform and larger?

Original grain sizes that are obliterated during the process of grain growth include smaller grains, such as those resulting from initial sedimentation or crystallization. As these smaller grains collide and merge due to thermal energy or mechanical processes, they become larger and more uniform in size. This phenomenon often occurs during processes like recrystallization in metamorphic rocks or during the sintering of ceramics. The result is a more homogenous microstructure with reduced grain size variation.