Basalt metamorphized is best described as which type of rock?

• A. Metamorphic
• B. Igneous
• C. Sedimentary
• D. Clastic

Answer: (A)

Basalt that has undergone metamorphism is described as metamorphic because metamorphism changes rocks in the solid state under heat and pressure, rearranging minerals and textures without melting. Basalt itself is an igneous rock formed from the cooling of lava, so its original composition is basaltic. When subjected to metamorphic conditions, the minerals recrystallize and align, producing a new rock with mineral assemblages and textures characteristic of metamorphic rocks—things like amphibolite or greenschist facies, depending on the degree of metamorphism. This is why it’s categorized as metamorphic rather than igneous or sedimentary. If it stayed igneous, it would simply be basalt; if it were sedimentary, it would require deposition and lithification of grains, which basalt under metamorphism does not involve.