Schist

Mica schist is a collective term for foliated metamorphic rocks. From gneiss they are distinguished by the retreat of feldspar and the frequent occurrence of certain, more characteristic minerals. Parent rock are mainly clay-rich rocks, so mudstones or argillaceous sandstones, they belong to the group of metapelites or Metapsammite.

Appearance and composition

Mica schist are medium - to coarse -grained metamorphic rocks with mostly high-visibility, parallel -aligned structure ( metamorphic parallel texture ). The proportion of the layered silicates (particularly muscovite and biotite subordinate also paragonite ) is above 50%, the feldspar is less than 20 %. At further Gemengteile next quartz may include garnet, staurolite, tourmaline and kyanite occur. The mineral grains are usually visible to the naked eye or at least with a magnifying glass, they can be several centimeters long (fruit shale, shale nodes ) in some cases.

The color of the mica schist is light to dark gray, but by weathering they may also appear brownish or reddish. The density is from 2.60 to 3.05 g / cm ³.

Depending on the occurrence of other mixture components, the types of mica schist are distinguished, such as quartz - mica schist, garnet - mica schist, staurolite - mica schist and others. Be distinguished from mica phyllites by the size of the minerals that can be seen in the case of phyllite only under the microscope.

Occurrence

Mica schist are found worldwide where the pressure and temperature conditions sufficient for their formation. For this reason, they are often found in the field of cratons or the inner zones of mountains.

In the Alps, mica is a common rock, such as in the Austrian Central Alps or in the Valais. In Germany there are deposits in the Erzgebirge, in the Bavarian Forest, at Osser, in Vorspessart ( near Aschaffenburg ) and in the Taunus. Other European deposits are located approximately in Spain (Sierra Nevada), in France ( Massif Central, Brittany ... ) or a large area on the surface pending in Norway, Sweden and Scotland. Outside Europe they occur, for example in many mountain ranges on, such as the Andes or the Himalayas, and form large areas as in the Brazilian and Canadian Shield.

Use

In construction, mica schist are sometimes used as platy blocks, such as floor coverings. High quality show, inter alia, the quarries of Fischbach (Taunus ). Good varieties are coming from countries outside Germany Fåvang in Norway.

In the Middle Ages mica was used for the production of millstones, which had to be rarely sharpened.