Foliation in geology refers to repetitive layering in metamorphic rocks. Each layer can be as thin as a sheet of paper, or over a meter in thickness. The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure.

What does foliated rock mean?

(Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned.

What does foliated and non-foliated mean?

Foliated metamorphic rocks have a layered or banded appearance that is produced by exposure to heat and directed pressure. Examples of foliated rocks include: gneiss, phyllite, schist, and slate. Non-foliated metamorphic rocks do not have a layered or banded appearance.