Granulite

Granulite form at crustal depths, typically during regional metamorphism at high thermal gradients of greater than 30 ℃/km. 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. Some assemblages such as sapphirine + quartz indicate very high temperatures of greater than 900 ℃.

They are medium to coarse–grained and mainly composed of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure.

Granulite is a popular choice for construction materials, as well as statues, monuments, and other artifacts. However, it may also been seen in work surfaces, such as laboratory bench tops due to its durable and chemically resistant nature. When ground, granulite is also used as an addition to soil to promote plant growth.

The granulite facies is determined by the lower temperature boundary of 700 +/− 50 °C and the pressure range of 2–15 kb. The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and Al2O3-rich pyroxenes. Transition between amphibolite and granulite facies is defined by these reaction isograds: amphibole -> pyroxene + H2O biotite -> K-feldspar + garnet + orthopyroxene + H2O. Hornblende granulite subfacies is a transitional coexistence region of anhydrous and hydrated ferromagnesian minerals, so the above-mentioned isograds mark the boundary with pyroxene granulite subfacies – facies with completely anhydrous mineral assemblages.