Hornfels are highly metamorphosed rocks, resulting from the contact between sedimentary, metamorphic, or igneous rocks with a hot magmatic body, like a lava flow or igneous intrusion. This metamorphic formation process is called contact metamorphism, where the original rock is altered directly by the heat of the magmatic body. The zone of contact metamorphism, referred to as the contact aureole, is localized from millimeters to kilometers in scale around the heat source, where heat-driven metamorphic intensity increases inwards of the aureole. Typically occurring at shallow depths, pressure lacks a role in the formation of hornfels. For this reason, they often lack any foliation or preferred orientation from compressional deformation. Since metamorphic intensity varies by radial distance within the aureole, there is a possibility that some hornfels may exhibit some pre-existing structural, bedding, or textural features from its parent rock closer to the outer parts of the aureole. Though some parent rock features can be retained, hornfels are generally massive, homogenous, hard, and fine-grained with sub-conchoidal fractures, and are commonly grey or black but can vary in colour depending on its protolith, making hand sample identification very difficult. This leaves classification to microscopic observations where fragmented equigranularity grains exhibit a distinct interlocking mosaic-like texture. However, due to varying protoliths, hornfels also vary in mineralogy and are generally classified as either pelitic, carbonate, or mafic hornfels. Pelitic hornfels are of sedimentary or metamorphic protolith, such as mudstone, slate, and shale, and typically contain biotite, quartz, potassium feldspar, cordierite, andalusite, or sillimanite as primary minerals. Carbonate hornfels originate from impure calcareous sedimentary rocks, like limestones, dolostones, or marble and can sometimes occur banded and bearing calc-silicate minerals, like diopside and wollastonite. Mafic hornfels are formed from mafic igneous rocks, such as basalts, andesites, and diabases and can vary in composition but are mainly comprised of plagioclase feldspars, amphibole, and pyroxenes alongside secondary minerals in veins and cavities, such as calcite and chlorite.