Metamorphic Processes & Textures

Degree of Metamorphism

• Intensity controls rock texture and mineral composition.
• Low-grade metamorphism ➜ rocks become more compact, denser.
• High pressures & temperatures ➜ minerals recrystallize into larger crystals.

Mineral Alignment & Foliation

• Sheet minerals (e.g., mica) and elongated minerals (e.g., hornblende) rotate until their longest dimension is perpendicular to stress.
• Preferred orientation produces layered/banded appearance = foliation.

Non-Foliated Rocks

• Rocks made of a single mineral with equidimensional crystals (e.g., calcite marbles) lack foliation.

Formation of New Minerals

• Metamorphism can create new minerals, especially where rocks contact large magma bodies.
• Hydrothermal solutions from late-stage magma crystallization drive this alteration.