# Hunsrück Slate

- Page: https://taslar.bumba.tr/en/stones/hunsruck-slate/
- Turkish: Hunsrück arduvazı
- Also known as: Hunsrück-Schiefer, Bundenbach slate
- Kind: Rock
- Classification: Rocks › Metamorphic rocks › Foliated
- Hardness (Mohs): 3–4
- Specific gravity: 2.7–2.8 g/cm³
- Colours: dark grey, bluish black, grey
- Composition: Slate formed by low-grade metamorphism of fine marine mud (fine micas and chlorite derived from clay minerals, with quartz). Many of its fossils are coated in a thin layer of pyrite (iron sulfide).
- Texture: Very fine-grained; splits into thin, flat sheets, which made it a sought-after roofing stone for centuries.
- Value ladder: 3/9 step, Building and industrial stone

Germany's roofing stone and fossil treasure: a slate holding 400-million-year-old sea creatures, their soft tissues sometimes preserved in gleaming pyrite.

The Hunsrück Slate is an Early Devonian (about 408–400 million years old) slate unit exposed in the Hunsrück and Taunus regions of western Germany. For centuries it was quarried for roofing. Its world fame, though, comes from its fossils: more than 260 animal species, often coated in a thin layer of pyrite and sometimes preserved with their soft tissues. This makes it a Konservat-Lagerstätte, a deposit of exceptionally preserved fossils.

## How does it form?

The Hunsrück Slate formed from fine mud laid down early in the Devonian (Late Pragian to Early Emsian, about 408–400 million years ago) in the Rhenohercynian sea, south of the ancient continent of Laurussia. The mud was later buried and lightly metamorphosed into slate that splits into thin sheets. The unit lies between the older Taunus quartzite below and younger sandstones above.

The exceptional preservation of its fossils needed special conditions: animals were buried quickly in oxygen-poor mud, decay slowed, and in an environment rich in sulfur and iron the surfaces of their bodies turned into pyrite. Pyritisation of this kind is rare in the fossil record. In some parts of the area the fossils are poorly preserved, showing that shallow, well-oxygenated waters also existed.

## What is it used for?

- **Roofing:** For centuries it was used on roofs as "Rhenish slate". Its use goes back to Roman times, and the first documented mining dates from the 14th century. Production revived after 1870–71 and declined from the 1960s because of cheaper synthetic and imported slate. By the 1990s only a single pit near Bundenbach was worked; after 1999, slate from Spain, Portugal, Argentina and China largely ended local mining.
- **Science:** The Hunsrück is one of the few marine Devonian fossil deposits with soft-tissue preservation. Its fossils are studied to understand life in Devonian seas; the first scientific paper on them was published by Ferdinand von Roemer in 1862.

## Where is it found?

The Hunsrück Slate crops out in a strip about 15 km wide and 150 km long, running from northwest to southeast. The fossil sites lie mostly south of the River Moselle and west of the Rhine. The main basins are around **Kaub**, **Bundenbach** and **Gemünden**, and the best-preserved fossils come from Bundenbach and Gemünden. Echinoderms are concentrated around Bundenbach, brachiopods in the northeast.

## How to recognise it

- A dark grey or bluish-black, very fine-grained stone that splits into thin, flat sheets.
- Fossils often show on the surface as thin reliefs coated in shiny, brassy-yellow pyrite.
- Most fossils found are starfish, brittle stars, crinoids (sea lilies) and trilobites.

## What determines its value?

As a roofing stone, its value lay in splitting into thin, flat and durable sheets, but from the 1960s it could not compete with cheaper synthetic and imported slate. Today its real value is scientific: pyritised fossils with preserved soft tissues are highly sought by museums and collectors. A fossil's value depends on how complete and well preserved it is and how rare the species is.

This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.

## Myths and misconceptions

- Myth: The shiny yellow coating on the Bundenbach fossils is gold. Fact: The coating is not gold but pyrite (“fool's gold”), an iron sulfide mineral. The fossils were pyritised because they were buried quickly in oxygen-poor mud rich in sulfur and iron.

## Curious questions

**Why are the Hunsrück fossils so well preserved?**

The animals were buried quickly in mud with very little oxygen, which slowed decay. In mud rich in sulfur and iron, the surfaces of their bodies turned into pyrite. This pyritisation preserved even soft tissues and gave the fossils their gleaming look.

## Did you know?

- In 1970 Wilhelm Stürmer, a physicist and radiologist at Siemens, used X-rays to study the slabs without opening them, imaging the fossils' soft tissues in detail for the first time.
- More than 600 small pits are known in the area, dug to extract roofing slate. Many of the finest fossils in museums were found by the miners who worked them.
- More than 60 species of crinoids (sea lilies) have been described from the Hunsrück Slate.

## Where is it found?

- Bundenbach, Hunsrück, Rhineland-Palatinate, Germany (Type locality): The best locality for exceptionally preserved fossils; Hunsrück fossils are also called “Bundenbach fossils”. Echinoderms (starfish, crinoids) are concentrated around here.
- Gemünden, Hunsrück, Rhineland-Palatinate, Germany (Major deposit): With Bundenbach, one of the two best localities for exceptionally preserved fossils.
- Kaub, Rhine valley, Rhineland-Palatinate, Germany (Known locality): One of the main depositional basins of the Hunsrück Slate; brachiopods dominate in the northeast of the basin.

## Sources

- [Hunsrück Slate](https://en.wikipedia.org/wiki/Hunsr%C3%BCck_Slate), Wikipedia
- [Slate](https://en.wikipedia.org/wiki/Slate), Wikipedia
- [Common rock densities](https://www.chemeurope.com/en/encyclopedia/Common_rock_densities.html), chemeurope.com (from Wikipedia, GFDL)
- [Bundenbach](https://en.wikipedia.org/wiki/Bundenbach), Wikipedia
- [Gemünden (Hunsrück)](https://en.wikipedia.org/wiki/Gem%C3%BCnden_(Hunsr%C3%BCck)), Wikipedia
- [Kaub](https://en.wikipedia.org/wiki/Kaub), Wikipedia


Source: https://taslar.bumba.tr/en/stones/hunsruck-slate/ · Licence: CC BY-SA 4.0