Final answer:
The question is about the characteristics of metamorphic rocks, particularly quartz-composed ones like quartzite, which can be fine to coarse-grained and show variable metamorphic grades.
Quartzite is a hard, acid-resistant rock formed from the metamorphism of quartz-rich sandstones or siltstones, and it can show banded textures and crystalline structures.
Step-by-step explanation:
The student's question pertains to the characteristics of metamorphic rocks, particularly those with a quartz composition that exhibit variability in metamorphic grade and grain size. Metamorphic rocks, such as quartzite, often display a crystalline texture and can range from fine to coarse-grained based on the conditions they are formed under.
Quartzite, for instance, originates from the metamorphism of quartz-rich sandstones or siltstones and can show thick bands or semi-continuous layers of minerals like quartz, feldspar, and mica.
Characteristics of some metamorphic rocks include medium to coarse-grained textures, banded and coarsely crystalline structures, and large, crystalline grains. When describing these rocks, terms like nonfoliated, medium-grained, and coarse-grained are frequently used. It's important to note that quartzite is highly durable, resistant to acid, and comes in various colors.
The transformation of these rocks often depends on temperature and pressure conditions during metamorphism, as shown by index minerals in metamorphosed shales which indicate the grade of metamorphism.