Igneous rocks with a two-stage intrusive-extrusive origin are recognized by a texture which is ____.
A) aphanitic
B) porphyritic
C) glassy
D) phaneritic
E) pyroclastic

Question

Quizplus · Accepted Answer

Porphyritic texture is characterized by large crystals (phenocrysts) surrounded by smaller crystals (groundmass). This texture can only be formed by a two-stage process where the magma cools and solidifies underground (intrusive) first, allowing large crystals to form, and then erupts onto the surface (extrusive) where the remaining magma cools rapidly, creating smaller crystals in the groundmass. Aphanitic, glassy, phaneritic, and pyroclastic textures do not necessarily indicate a two-stage origin.

Igneous Rocks with a Two-Stage Intrusive-Extrusive Origin Are Recognized by a Texture