There are several differences between metamorphic rocks that are foliated and those that are not foliated. When intense heat is added to a parent rock, it then transforms into a metamorphic rock which may or may not become foliated. Differences such as texture, parent rock source, appearance and pressure applied during recrystallization can indicate whether or not a metamorphic rock is foliated.
Recognize the characteristics of foliated rocks. Typically, foliated rock has a flaky or ridged appearance that is quite prominent and easy to notice. This flaky and ridged appearance is due to the rock having a flat or parallel mineral arrangement. Heat and pressure can cause the minerals to be arranged and banded in a manner that gives the rock the foliated appearance. This layered appearance indicates that it is indeed a foliated rock.
Learn about the characteristics of non-foiated rocks. Unlike foliated rock, non-foliated rock does not have a layered appearance and does not have the same flaky look. Non-foliated rocks typically break off into chunks, as opposed to being split into layers. For example, marble is a non-foliated rock that comes from its parent rock limestone.
Learn what foliation indicates about the rock's formation. When a rock is heated and under pressure, the process of crystallization begins and will change the composition of a rock. When unequal amounts of heat and pressure form on a metamorphic rock, it will result in the formation of a foliated rock. If the heat and pressure during crystallization are equal, then a non-foliated rock will form.
Look for examples of foliated and non-foliated rocks around your home. It may be surprising to discover that these are very common rocks that can be found in some form around your house. For example, slate, phyllite and schist are examples of foliated rocks and may be used in outdoor decorating or gardening. Quartzite, marble and anthracite coal are examples of non-foliated rocks.