High Grade Metamorphic Rocks: Identifying Minerals

What is a high grade metamorphic rock?

A) A rock formed from quartz and feldspar

B) A rock formed from calcite and dolomite

C) A rock containing garnet and staurolite

D) A rock composed of halite and gypsum

Answer:

C) A rock containing garnet and staurolite

High grade metamorphic rocks are rocks that have undergone intense heat and pressure, leading to the formation of new minerals. In the case of high grade metamorphism, minerals like garnet and staurolite are indicative of the intense conditions these rocks have endured.

During the metamorphic process, minerals such as garnet and staurolite are formed under high temperatures and pressures, distinguishing them from minerals that can form under lower grade metamorphic conditions. These minerals are often seen as porphyroblasts within a fine-grained matrix, highlighting the high grade nature of the rock.

For example, gneiss, a common high grade metamorphic rock, often exhibits bands of light and dark minerals due to intense metamorphism. The presence of minerals like garnet and staurolite within the matrix of gneiss is a clear indication of the high grade metamorphic conditions that were present during its formation.