Mineral inventory and rock description
Tonalites are mostly gray to light dark. This depends on the number of light or dark minerals in the rock. However, tonalite is much more basic than granite and does not contain any alkali feldspar . Tonalites contain quartz , plagioclase , hornblende , biotite and rarely augite . They are medium to coarse-grained. As an accessory, they contain orthite , apatite , zirconium , titanite and magnetite .
Naming and occurrence
The name of the rock goes back to the Tonale Pass in northwestern Italy and was introduced to rock science by Gerhard vom Rath in 1864 after this type locality . It lies on the Periadriatic Seam (also known as the Insubric Line , a geological fault line important for southern Europe ). It is a leucocratic (light) tonalite with abundant biotite , which occurs in the eastern part of the Adamellomassif and which goes back to a huge intrusion of the tertiary period.
Tonalites form in subduction zones and on a significant scale on the Pacific coast of America, but also in the south of Norway . There are few occurrences in Germany: In the Fichtelgebirge there is an occurrence of tonalites, the so-called Redwitzites from Seußen and Wölsau near Marktredwitz . Tonalite is also found in the Märkerwald near Groß-Bieberau and in the Bavarian Forest .
Tonalite are used in solid construction, as brick, facade panels, floor and stair coverings and in road construction as gravel and road surface. This natural stone was preferred as a tombstone in Germany in the 1950s and 1960s. Tonalite can be polished and is frost-resistant.
- Friedrich Müller : International Natural Stone Index (INSK), 10th vol., 3rd edition. Ebner Verlag, Ulm 1993.
- Walter Maresch, Olaf Medenbach, Hans D. Trochim: Steinbach's natural guide rocks. Munich 1996, ISBN 3-576-10699-5 .
- Walter Maresch, Hans-Peter Schertl, Olaf Medenbach: Rocks. Systematics, determination, development 2. completely revised. Edition. Schweizerbart, Stuttgart 2014, ISBN 978-3-510-65285-3 .
Type of natural stone
- Verde Mergozzo (Italy, Baveno )
- Adamellite (Italy, Adamellomassiv)
- Walter Maresch among others: Steinbach's natural guide rocks. 1996, p. 50.