What kind of rock is andesite


Author: Torsten Purle (steine-und-minerale.de) | Last update: 05/05/2021

Andesite - properties, formation and use

English: andesite | French: andésite

Andesite - rock of the year 2020/21

The rock andesite was first mentioned in his remarks by Christian Leopold Freiherr von Buch (1774 to 1853) "About elevation craters and volcanoes" described in 1835. The German geologist named the rock after the Site in the Andes in South America. Alternatively, andesite is called islandite - after the occurrence of the rock on the island of Iceland in northern Europe.

Properties of andesite

Definition: Andesite is defined in geology as an igneous rock of extrusive origin (alternatively: effusiva, effusion rock, volcanic rock) that is of intermediate classification. Due to its composition, andesite is the pouring equivalent of diorite.

Andesites are dark rocks; primarily gray, black, gray or brown with a tinge of reddish or purple going, determined by the mineral composition, i.e. mixed parts, of andesite.

The mixed parts, in turn, are a Criterion to distinguish andesite from visually similar basalt to distinguish. Both rocks are dark in color - but andesite is characterized by a proportion of dark minerals that is less than 35%. In comparison, more than 35% of basalts are made up of dark mixtures.

The main component of andesite is up to 53% quartz, which is involved in the structure of the rock, followed by plagioclase feldspar.
Subordinately, andesite contains representatives of the pyroxenes (augite, bronzite, hypersthene), amphiboles as well as mica, olivine and magnetite, which can be recognized without aids. The rock matrix often contains idiomorphic inserts of augite, hornblende and biotite, which often results in a porphyry structure - which is particularly common in Icelandic andesite - islandite.

Andesite is a fine to medium-grained rock, the aggregates of which are densely packed; Often a direction of flow is recognizable and there are cavities that are sometimes lined with minerals.

With a density of 2.5 to 2.8 g / cm3 andesite is a comparatively light rock.

Formation and distribution of andesite

Andesite is a volcanite that is formed during the cooling of lava flows with an intermediate composition or in subduction zones, where mantle rocks are regularly melted down.

Significant andesite deposits are found in Scotland; Rovaniemi / Finland and Iceland; Hunsrück, Thuringian Forest, Flechtingen, Halle, Eifel / Germany; Poland; Banská Bystrica / Slovakia; Sardinia, Bozen, South Tyrol / Italy; Carpathian Mountains / Romania; Peloponnese / Greece; Spain just like in Szentendre / Hungary; Uzbekistan; Indonesia; In addition, Shikoku / Japan; Borneo / Indonesia; New Zealand; Andes in South America; Chihuahua / Mexico; California, Michigan, Montana / USA; British Columbia / Canada.

Use and meaning of andesite

Andesite is used in particular as gravel for roads, grit or in sculpture. Due to the importance for the economy and the versatile use of andesite in everyday life, the Professional Association of German Geoscientists (BDG) has chosen andesite as the rock of the year 2020.

Also interesting:
⇒ Alexander von Humboldt and the minerals
⇒ Characteristics of rocks: main and secondary parts
⇒ grit

⇒ book, L. v. (1835): About elevation craters and volcanoes. IN: Annals of Physics and Chemistry.
⇒ Pellant, C. (1994): Stones and Minerals. Ravensburger nature guide. Ravensburger Buchverlag Otto Maier GmbH
⇒ Maresch, W., Medenbach, O .; Trochim, H.-D. (1987): The colored natural guide rocks. Mosaik Verlag GmbH Munich
⇒ Murawski, H. (1992): Geological Dictionary. Ferdinand Enke Verlag Stuttgart