Non-foliated metamorphic rocks, such as marble, lack bands or layers.
Metamorphic rocks form beneath the earth’s crust, where they experience high temperatures and pressures as well as ongoing chemical processes. There are two types of metamorphic rocks: foliated and non-foliated.
Metamorphic rocks such as quartzite, amphibolite, hornfels and marble are examples of non-foliated rocks. They have a non-banded and non-layered appearance.
Schist, gneiss, slate and phyllite are examples of foliated rocks, which have a banded or layered appearance.
Non-foliated rocks form through recrystallization of single-mineral sedimentary rocks, usually those that have been touched by magma. This happens beneath the earth’s crust, usually less than 20 kilometers deep. Foliated rocks can occur on the earth’s surface due to weathering or uplift.
Non-foliated rocks are usually hard and dense. They can possess swirls of color due to impurities in the original sedimentary rock that did not participate in the recrystallization.
A non-foliated rock usually occurs near deposits of its parent, sedimentary rock. For instance, marble is a non-foliated metamorphosed version of limestone and usually occurs near limestone deposits. Similarly, quartzite typically occurs near quartz sandstone, and hornfels is often found near shale.