What is a primary feature developed during metamorphism that indicates the direction of stress?

• A. Foliation
• B. Porosity
• C. Cleavage
• D. Grain size

Answer: (A)

When rocks are subjected to directed pressure during metamorphism, minerals realign into a layered, planar fabric called foliation. This happens as minerals like micas or platy grains rotate and recrystallize so they stack in sheets. The crucial point is that the foliation planes form perpendicular to the direction of the maximum compressive stress, so by looking at the orientation of the foliation you can infer the stress direction—the stress is along the normal to those planes.

Porosity is just empty space within the rock and doesn’t reveal stress direction. Grain size can change with metamorphic grade but doesn’t directly indicate the direction of the applied pressure. Cleavage is another stress-related fabric, but foliation is the more general and diagnostic feature for showing the stress direction in many metamorphic rocks.