Amphibolite is a foliated metamorphic rock composed principally of hornblende and plagioclase. It forms_________ .
A)by regional metamorphism of volcanic rocks such as basalt
B)by contact metamorphism of sandstone along the contact with a granitic batholith
C)by gouging and crushing of limestone along a fault
D)by the impact of an asteroid on interbedded sandstone and shale

Question

Quizplus · Accepted Answer

Amphibolite is typically formed by regional metamorphism of volcanic rocks such as basalt. The high temperature and pressure conditions that occur during regional metamorphism cause the minerals in the original rock to recrystallize and reorient themselves into a foliated structure. Hornblende and plagioclase are two common minerals that are stable under these conditions and thus are often found in amphibolite. Contact metamorphism (B), gouging and crushing (C), and impact metamorphism (D) can also form metamorphic rocks, but they typically do not result in the formation of amphibolite.

Amphibolite Is a Foliated Metamorphic Rock Composed Principally of Hornblende