Final answer:
The most widely distributed type of metamorphic rock is schist, a medium- to high-grade metamorphic rock with a foliated texture. It forms from the alteration of protoliths like shale under high temperatures and pressures, resulting in significant changes to its mineralogy and texture.
Step-by-step explanation:
The most widely distributed type of metamorphic rock is schist. Metamorphic rocks, such as schist, are produced through the alteration of pre-existing rocks (known as protoliths) under the influence of high temperatures and pressures below Earth's surface. This process can change physical or chemical properties, resulting in different textures and structures in the rock. Schist is characterized by its foliation, meaning it has a layered or banded appearance due to the arrangement of mineral grains within the rock. Unlike sedimentary rocks like sandstone, or the non-foliated metamorphic rock quartzite, schist is known for its high degree of metamorphism, which leads to the alignment of minerals and a platy texture.The process of metamorphism begins with a protolith, which in the case of schist, often starts as shale or mudstone. As these rocks are subjected to increased levels of heat and pressure, they transform through different grades, starting from slate, progressing to phyllite, and eventually becoming schist as the metamorphic grade increases. Schist typically displays medium- to high-grade metamorphism, indicating it has undergone significant alterations in its mineralogy and texture.In conclusion, schist is the main answer for the most widely distributed type of metamorphic rock. Its prevalence is due to the abundant original materials like shale that can metamorphose into schist and the widespread geologic conditions that facilitate such transformations on Earth.