Here's why:

* Foliation is a layered or banded texture that develops in metamorphic rocks due to pressure and heat. This pressure causes the minerals within the rock to align in a parallel direction.

* Non-foliated metamorphic rocks lack this layered texture. They form under conditions where the pressure is more uniform or where the minerals are not easily aligned.

Examples:

* Foliated metamorphic rocks: Slate, schist, gneiss

* Non-foliated metamorphic rocks: Marble, quartzite, anthracite coal

Let me know if you have any more questions!