Borden slate

What is written on the plate:

Borden slate

An alternating deposit of fine-grained graywackes and clay shales is called Borden shale. This sediment was transported by turbidity currents, following gravity, from an oversteepened basin slope and came to rest on the deep shelf. Sands and clays settled successively from the sediment cloud. Folding and metamorphism can be seen in the shine of the clay slates and the schistosity can be read.

Ziegenrück Formation, Lower Carboniferous, Döbritz hardstone plant, Thuringian Slate Mountains, ca. 350 Ma

Borden slate

Location: Döbritz hardstone plant, Thuringian Slate Mountains

Age: ca. 350 million years

Hartsteinwerk Döbritz

Image: Google Maps

Borden shale is a variety of the rock slate. Shale is a collective term for various tectonically deformed and partly also metamorphic sedimentary rocks, which are characterized by their excellent cleavage along closely spaced parallel planes, the so-called schistosity planes. Shale is used in modern petrography mainly for tectonically stressed rocks. Nevertheless, the traditional term shale continues to be used for undeformed, fine-grained sedimentary rocks that exhibit similar fissurability.

Borden shale is a slabby rock that splits well. It consists of many superimposed plates and foliated structures that exhibit foliation, or a succession of slaty surfaces. The mineral composition of the Borden shale is mainly dominated by clay minerals, quartz, feldspars, as well as accessory minerals such as mica group minerals (like biotite and muscovite), chlorite, kyanite/disthene, hematite, glaucophane, actinolite, and garnet. This mineral emplacement ensures that the rock is parallel aligned and splits well along the schistosity surfaces.

Borden shale varies in color depending on its mineral composition and the minerals it contains. Colors range from shades of gray (e.g., amphibole shale) to black (clay shale) to shades of green (green shale) to blue, silver, and white (white shale).

The formation of shale, including Borden shale, occurs through tectonic deformation and folding of sedimentary rocks. In the process, the rocks are reshaped under pressure and elevated temperatures. Clay shale, for example, is formed from mudstone that becomes a dense, fine-clastic rock under pressure and elevated temperatures. Crystalline shales are metamorphic rocks that have been transformed by high temperatures and pressure and have crystalline structures. The formation of slate is closely related to the geological history of the particular region.

Borden slate is used in various fields. Due to its good cleavage along the slate surfaces, it is often used as a building material for roofing, facade cladding, flooring and walls.

Location of the rock Migmatite in the stone mine Döbritz

Image: Thomas Voigt