Amphibolite is a foliated metamorphic rock composed principally of hornblende and plagioclase.How does it form?
A)by contact metamorphism of quartzose sandstone cut by a granitic batholith
B)by regional metamorphism of volcanic rocks such as andesite and basalt
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 forms by regional metamorphism of volcanic rocks such as andesite and basalt. The presence of hornblende and plagioclase in the rock indicates that it formed from a precursor rock that contained these minerals, such as volcanic rocks. Contact metamorphism (choice A) involves the heating of rocks by an igneous intrusion, which can lead to the formation of non-foliated rocks such as marble or hornfels. Gouging and crushing of limestone (choice C) would not typically result in the formation of amphibolite. Finally, the impact of an asteroid (choice D) could generate high pressures and temperatures, but typically results in the formation of impact breccias rather than a particular metamorphic rock like amphibolite.

Amphibolite Is a Foliated Metamorphic Rock Composed Principally of Hornblende