Hornfels

Classification：Metamorphic Rock

It is formed by low pressure and high temperature heat contact metamorphism. It has a fine granular crystalline structure and a massive structure.

Hornfels usually refers to a metamorphic rock produced by contact metamorphism.
Hornfels was originally a sedimentary rock. Due to the intrusion of magma, the release of heat caused the sedimentary rocks to be recrystallized and made the earlier sedimentary strata completely transformed into hard, often chert - like rocks. Common mica hornfels, felsic hornfels, calcium silicate hornfels type.
Hornfels is foliated structure with conchoidal fracture. Hornfels contains standard metamorphic minerals such as cordierite, andalusite and sillimanite, as well as new minerals such as quartz, biotite, magnetic ore, feldspar, hornblende and pyroxene.

Concept:
Hornfels also known as hornfels, formed by high temperature thermal contact metamorphism, refers to with fine grained crystalloblastic texture and massive structure. The protolith is mainly clastic rock, siltstone, igneous rock and limestone pyroclastic rocks. After metamorphism, they all recrystallized, and generally do not have a structure of change. The rocks are mainly composed of feldspar, mica, hornblende, quartz and pyroxene, as well as metamorphic minerals such as sillimanite, cordierite, andalusite and pomegranate. [2]

Features：
Hornfels is a hornfels structure and massive structure of rock. The surface of Hornfels is usually dark, sometimes light, dense and hard. The fine mineral composition of Hornfels is usually identified only under a microscope. Besides the partial migration of some free components (such as water and carbon dioxide) in the sedimentary rocks, the standard Hornfels is rarely accompanied by chemical changes. Therefore, the chemical composition of the Hornfels is only related to the composition of the original sedimentary rocks and is based on the original. The properties of the initial sedimentary rocks can also be predicted.
The mineral composition of Hornfels:
A continuous series of shale and limestone derived from different sedimentary rocks in various Hornfels containing some marl mixture is the most significant. In chemistry, this series is mainly composed of the following components: silica SiO2, alumina Al2O3, calcium oxide CaO, ferrous oxide FeO and Magnesium Oxide MgO.
Many of the main minerals of Hornfels, such as quartz, feldspar, pyroxene, calcite and calcite, are usually equiaxed grains, even the plate and columnar habits of mica and amphibole, which are greatly less significant in the schist and igneous rocks than in the Hornfels, and have no or very indistinct preferred orientation. Therefore, most of Hornfels is made up of equiaxed and non aligned particles embedded in each other, and its structure is called Hornfels like structure. There are several kinds of minerals formed by contact metamorphism. The most notable ones are andalusite and cordierite. They usually become large porphyritic dendrite and filled with small enclaves. Other minerals, such as biotite, muscovite, tourmaline, garnet, perlite and andalusite, can also become porphyritic in some environments. Therefore, many of Hornfels's features is combined with coarse structure metacrystal and granoblastic.
Because deformation does not play any role in the evolution of typical Hornfels, even residual Hornfels is often found in completely metamorphic. It is very easy to recognize, such as almond shaped structure porphyritic structure formed in the residual traces of many causes in the Hornfels volcano. The mudstone bedding can be retained in the muddy Hornfels, which is characterized by the different size and quantity of the mica and the andalusite. 

Common types:
According to the main mineral components, Hornfels can be divided into mica corner rock, long angled rock, calcium siliceous corner rock, basic corner rock, magnesia corner rock and so on. It can also be named according to the main mineral and characteristic metamorphic minerals, such as cordierite black cloud parent rock and long angled rock.