transition : Idioms & Phrases
phase transition
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noun a change from one state (solid or liquid or gas) to another without a change in chemical composition
state change; phase change; physical change.
WordNet
Transition rocks
(Geol.) , a term formerly applied to the lowest uncrystalline stratified rocks (graywacke) supposed to contain no fossils, and so called because thought to have been formed when the earth was passing from an uninhabitable to a habitable state.
