Porphyritic Textures with Fine-Grained Groundmasses
Many rocks with an overall fine-grained texture display scattered minerals that are more than 1 mm across. This porphyritic texture indicates that the magma sat and cooled a bit below the Earth's surface, thus giving time for the large crystals to grow, before erupting onto the surface and cooling very quickly. The large crystals are termed phenocrysts while the aphanitic rest of rock is called the groundmass. The rocks below cover mafic, intermediate, and felsic compositions (top to bottom).
|
|
