Granulites form at crustal depths, typically during regional metamorphism at high thermal gradients of greater than 30 °C/km.[2] In continental crustal rocks, biotite may break down at high temperatures to form orthopyroxene + potassium feldspar + water, producing a granulite. Other possible minerals formed at dehydration melting conditions include sapphirine, spinel, sillimanite, and osumilite.