Classification of Metamorphic Rocks

Classification of Metamorphic Rocks

• Metamorphic rocks are categorized based on composition and texture.

Key Terms and Definitions

• Foliation: A planar fabric element in metamorphic rocks.
• Lineation: A linear fabric element observed in the structure of metamorphic rocks.
• Schistosity: Characterized by aligned minerals visible to the naked eye, indicating coarse grain.
• Gneissosity: Exhibits poorly-developed schistosity or is layered due to metamorphic processes.

Types of Metamorphic Rocks

• Slate: A compact, very fine-grained rock with prominent cleavage, possessing dull freshly cleaved surfaces.
• Phyllite: Contains schistosity with fine phyllosilicates that provide a silky sheen, although the minerals are not typically visible to the naked eye.
• Gneiss: A metamorphic rock with a distinctive gneissose structure, marked by bands of different minerals.
• Granofels: Lacks preferred orientation, resulting in a more homogeneous appearance.
• Hornfels: A type of granofels, typically fine-grained and compact, usually found in contact aureoles from thermal metamorphism.
• Marble: Composed primarily of calcite or dolomite, often formed from limestone or dolostone protoliths.
• Quartzite: Dominantly made up of quartz, usually derived from sandstone protoliths.
• Amphibolite: A metamorphic rock rich in hornblende and plagioclase minerals.
• Eclogite: Notable for its green and red coloration, containing clinopyroxene and garnet, typically originating from basalt.
• Blueschist: Characterized by blue amphibole; formed from metamorphosed mafic igneous rock or mafic graywacke.
• Serpentinite: An ultramafic rock altered at low grades, largely comprising serpentine.

Special Characteristics

• Porphyroblastic: Describes rocks with one or more large metamorphic minerals called porphyroblasts that grow significantly larger than surrounding crystals.

Prefixes Indicating Parent Material

• Ortho-: Prefix used for rocks with an igneous parent origin.
• Para-: Prefix indicating a sedimentary parent material.

Explore the classification of metamorphic rocks based on their composition and texture. Learn about key terms such as foliation, schistosity, and various types including slate, phyllite, and gneiss. This quiz will enhance your understanding of the fundamental characteristics that differentiate these rocks.