In geology, a megacryst is a crystal or grain that is considerably larger than the encircling matrix. They are found in igneous and metamorphic rocks.[1] Megacrysts can be further classified based on the nature of their origin, either as:[2]
- Phenocrysts, which crystallize in molten rock material (lava or magma) and are hence an earlier crystallization than the matrix in which they are embedded
- Porphyroblasts, which develop in solid rock as the result of metamorphism or metasomatism