Texas A&M University (TAMU) GEOL101 Principles of Geology Exam 1 Practice Exam

The classification of low and high grades in metamorphic environments is fundamentally based on temperature and pressure conditions. Metamorphism occurs when pre-existing rocks undergo changes due to elevated temperatures and/or pressures within the Earth, leading to the formation of metamorphic rocks.

Low-grade metamorphism typically occurs at lower temperatures and pressures, generally resulting in the preservation of original rock textures and the formation of minerals stable at these conditions, like chlorite or sericite. In contrast, high-grade metamorphism takes place under significantly higher temperatures and pressure, which can lead to the formation of new minerals such as garnet or kyanite and often results in distinct textural changes in the rock.

While the presence of specific minerals and visual textures do contribute to the identification of the metamorphic grade, they are ultimately the manifestations of the underlying temperature and pressure conditions under which metamorphism occurs.