Fruchtschiefer is a local variety of contact metamorphic rock

Metamorphic rock

Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

 that is derived from argillite

Argillite

An argillite is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts of silt-sized particles. The argillites grade into shale when the fissile layering typical of shale is...

.

Formation and mineral content

Fruchtschiefer is formed under very low pressure (low grade metamorphic rock) and temperatures of ca. 500 °C. At these temperatures cordierite

Cordierite

Cordierite or iolite is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: 2 to 2...

 grows to the size of grains of corn, which is where its name comes from; Frucht being German for "corn" (as well as "fruit"). It contains the following minerals: cordierite

Cordierite

Cordierite or iolite is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: 2 to 2...

, muscovite

Muscovite

Muscovite is a phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a highly-perfect basal cleavage yielding remarkably-thin laminæ which are often highly elastic...

, potassium feldspar, quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

, biotite

Biotite

Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...

 and hornblende

Hornblende

Hornblende is a complex inosilicate series of minerals .It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....

.

Occurrence

Fruchtschiefer occurs in Germany as contact metamorphic rock in the Harz

Harz

The Harz is the highest mountain range in northern Germany and its rugged terrain extends across parts of Lower Saxony, Saxony-Anhalt and Thuringia. The name Harz derives from the Middle High German word Hardt or Hart , latinized as Hercynia. The legendary Brocken is the highest summit in the Harz...

, Ore Mountains

Ore Mountains

The Ore Mountains in Central Europe have formed a natural border between Saxony and Bohemia for many centuries. Today, the border between Germany and the Czech Republic runs just north of the main crest of the mountain range...

, Odenwald

Odenwald

The Odenwald is a low mountain range in Hesse, Bavaria and Baden-Württemberg in Germany.- Location :The Odenwald lies between the Upper Rhine Rift Valley with the Bergstraße and the Hessisches Ried in the west, the Main and the Bauland in the east, the Hanau-Seligenstadt Basin – a subbasin of...

 and Vogtland

Vogtland

The term Vogtland refers to a region reaching across the German free states of Bavaria, Saxony and Thuringia and into the Czech Republic . The name of the region contains a reference to the former leadership by the Vögte of Weida, Gera and Plauen, which translates approximately to advocates or lord...

. The best known deposits are those near Theuma and Tirpersdorf dating to the Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

. Rocks quarried here have been used well beyond the local region.

Use

The main traditional application is in the form of rough split masonry products of a wide variety. Fruchtschiefer from Theuma is also split or ground for use as facade slabs and plinth facings. Amongst the architectural components made in this material are window and door surrounds, columns and steps. Occasionally it is used for artistic or sculptural purposes. It was also used as canal lock and well covers as well as containers for galvanised baths

Galvanization

Galvanization is the process of applying a protective zinc coating to steel or iron, in order to prevent rusting. The term is derived from the name of Italian scientist Luigi Galvani....

 and acids.

The use of Theuma Fruchtschiefer can be traced back to the Middle Ages

Middle Ages

The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

. Examples include slabs in the crypt of St. John's Church in Plauen

Plauen

Plauen is a town in the Free State of Saxony, east-central Germany.It is the capital of the Vogtlandkreis. The town is situated near the border of Bavaria and the Czech Republic.Plauen's slogan is Plauen - echt Spitze.-History:...

(built 1122), which date to the 14th century.