Siltschiefer

What is written on the plate:

Siltschiefer

This rock was deposited in the early Ordovician on the Gondwanan shelf in water depths greater than 200 meters. Silt and clay originated from the turbidity of ocean water carried in by rivers. During the Variscan mountain building the sedimentary rock was transformed to a silty schist by increasing pressure and temperature. The mica formed from the clay minerals
mica rearranged themselves in the slate surfaces.

Phycoda shale, Ordovician, Schwarzatal, Thuringian Slate Mountains, ca. 490 Ma

Siltschiefer

Location: Schwarzatal, Thuringian Slate Mountains

Age: ca. 490 million years

Schwarzatal

Image: Thomas Voigt

Siltschiefer is a rock that belongs to the group of slates. To describe the rock Siltschiefer, it is first important to understand the term "slate". Shale is a collective term for various tectonically deformed and partially metamorphic sedimentary rocks [1External link]. These rocks are characterized by their excellent cleavage along closely spaced parallel planes, called schistosity planes, formed by deformation. Silty shale is a specific type of shale that consists of fine-grained material.

When looking at Siltschiefer, it is noticeable that it consists of many superimposed plates and flake-like structures. The mineral arrangement in silty slate shows either a linear structure (lineation) or a sequence of slate surfaces (foliation). Siltshale is formed by the metamorphic alteration of source rocks such as argillaceous shale, siltstone or mudstone under high pressure and high temperatures. These alteration processes produce new mineral phases and the characteristic properties of silty shale, such as its fissility and fine-grained structure [2External link].

Siltschiefer usually exhibits a gray to black color, but can also have other hues such as greenish, bluish, or brownish. The exact color depends on the minerals contained, which can occur in the silty shale. In addition to clay minerals, siltshale may also contain quartz, feldspars, mica, chlorite flakes, heavy minerals, rutile crystals, small cubes of pyrite, and even fossils [6External link]. Due to its composition and structure, silty shale has good resistance to weathering and is therefore versatile.

Siltschiefer is used in various fields. Due to its excellent splitting ability, it is often used as a building material for roofs, facade cladding, flooring and stairs. The thin slabs of silt slate can be easily worked and laid in a variety of ways to create aesthetically pleasing surfaces. In addition, silt slate is also used for decorative purposes, such as wall cladding, art objects or gravestones [7External link].

Location of the silty slate near the village of Schwarzatal

Image: Thomas Voigt