Magnetite-Skarn

Magnetite skarn is an interesting formation formed by the combination of magnetite and skarn. Magnetite, also known as magnetite or magnetite ironstone, is an iron oxide mineral with the chemical formula Fe3O4. It belongs to the mineral class of oxides and hydroxides and crystallizes in the cubic crystal system. Magnetite frequently forms octahedral crystals whose most common faces are {111}, but more rarely faces {110} or {100} occur. It shows indistinct cleavage along (111) and has a black color and a faint metallic luster.

Skarn, on the other hand, is a group of metamorphic or metasomatic rocks characterized by their mineralogical composition of predominantly calcium-rich silicates. They are usually formed during the intrusion of magmas into carbonate-rich rock strata such as limestone or dolomite, but can also form in various rock types without magmatic processes. Skarns are often mineralized and can form significant ore deposits for various metals. The term "skarn" was originally introduced by Alfred Elis Törnebohm to describe garnet-pyroxene rocks in the Persberg deposit in Sweden.

The combination of magnetite and skarn in magnetite skarn rocks results in a special composition and structure. Magnetite can occur in skarn rocks as inclusions, veins, or as a reaction between the magnetite and the surrounding skarn material. These rocks may contain a variety of minerals, including pyroxenes, garnets, diopside, wollastonite, and other silicates. The exact composition of magnetite skarns can vary depending on the specific geologic setting.

Magnetite skarn rocks are often economically important because they can host significant ore deposits for various metals. For example, copper, iron, or molybdenum deposits may be contained in magnetite skarn rocks. However, the exact extent and quality of these deposits varies from deposit to deposit.

Entrance to the Schwarzer Crux visitor mine

Image: Thomas Voigt