Mica Slate

What is written on the plate:

Mica Slate

This biotite-mica schist contains besides biotite and quartz also hornblende and feldspar. It thus shows transitions to a gneiss. The rock was probably formed from an iron-rich, impure mudstone or a tuff by metamorphic alteration at about 450° C and at a depth of 30-40 km. The schistosity was also created during this process. It belongs to a large complex of metamorphic rocks, which is called the Central German Crystalline Zone is designated.

Ruhla Group, Lower Devonian, Ruhla Station, Thuringian Forest, approx. 400 Ma

Mica Slate

Location: Ruhla train station, Thuringian Forest

Age: ca. 400 million years

Ruhla

Image: Google Maps

Mica schist is a schistose metamorphic rock belonging to the group of metapelites or metapsammites. It is formed by the alteration of clay-rich rocks such as mudstones or argillaceous sandstones. Compared to gneiss, mica schist is characterized by the recession of feldspar and the frequent occurrence of certain minerals.

Mica schist exhibits a medium to coarse-grained structure, with the metamorphic minerals showing a distinct parallel texture. The proportion of phyllosilicates, especially muscovite and biotite (occasionally paragonite), exceeds 50%, while the proportion of feldspar is less than 20%. In addition to quartz, garnet, staurolite, tourmaline, and disthene may be present, as well as other gemstones. The mineral grains are usually visible to the naked eye or at least under magnification and can reach a length of several centimeters.

The color of mica schist varies from light to dark gray. Due to its high content of mica minerals, it exhibits a characteristic shimmering luster. The microstructure of mica schist is medium to coarse flaky and has a striking parallel texture that gives the rock a linear appearance.

Mica schist occurs worldwide, but in Germany it is particularly common in the Alps, the Fichtelgebirge, the Bavarian Forest, the Erzgebirge, and the Black Forest. A well-known location for mica schist in Germany is the Osser Massif, which is located in the Bavarian and Upper Palatinate Forests and is distinguished from the surrounding granites and gneisses by its mica schist and quartzite composition.

In terms of its formation, mica schist originated from clayey deposits that were transformed under high temperatures and pressures in the earth's interior. This metamorphic transformation transformed the clayey source rocks into mica schist, producing the characteristic parallel texture and high percentage of mica minerals.

Mica schist finds various applications in the construction industry and as a material. Due to its cleavage along the slate faces, mica slate is often used as roof and facade cladding. In addition, it is also used as flooring, wall cladding, stair treads, countertops, and in cast stone production.

Location of the mica slate near the village of Ruhla

Image: Thomas Voigt