What Process Forms Rocks with Porphyritic Texture?

A porphyritic texture is developed when magma that has been slowly cooling and crystallising within the Earth's crust is suddenly erupted at the surface, causing the remaining uncrystallised magma to cool rapidly. This texture is characteristic of most volcanic rocks. ... This texture is exhibited by some volcanic rocks.

How do igneous rocks with porphyritic textures form quizlet?

A porphyritic texture forms when a rock has had two different stages of cooling resulting in two distictly different crystal sizes. Large crystals are called Phenocrysts and form first by cooling slowly, they are surrounded by a finer grained groundmass which cooled faster.

What is porphyritic structure?

In feldspar: Crystal structure. (A porphyry is an igneous rock containing conspicuous crystals, called phenocrysts, surrounded by a matrix of finer-grained minerals or glass or both.) In most rocks, both alkali and plagioclase feldspars occur as irregularly shaped grains with only a few or no crystal faces.