Hornblendegneis

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Hornblendegneis

Like granites, gneisses consist of quartz, feldspar and mica. They also often contain minerals newly formed during metamorphism (e.g. garnet, sillimanite, staurolite or amphibole). The minerals are enclosed in a foliation in which biotite and hornblende sprout. Gneisses can be formed from granites as well as from sedimentary rocks by metamorphism. The source rock of this gneiss was a diorite, which was transformed at about 450°C at a depth of 20 km.

Kyffhäuser crystalline, Rothenburg, Kyffhäuser,
Diorite: ca. 400 Ma, metamorphism to gneiss: 340 Ma

Hornblendegneis

Location: Rothenburg, Kyffhäuser

Age: ca. 400 million years

Rothenburg, Kyffhäuser

Image: Google Maps

Hornblende gneiss is a metamorphic rock with a parallel texture containing more than 20% feldspar. It is formed by metamorphism, which transforms rocks under high pressure and temperature. Gneiss is formed from parent material that is overlain by many layers of rock. To reach the surface, either the overlying material must have eroded or the deeper layers were lifted to the surface by tectonic movements [1External link].

Hornblende gneiss is common throughout the world and is often found in the ancient cores of continents, called cratons, where it has been exposed by deep erosion. These rocks have usually undergone several stages of metamorphism, known as regional metamorphism. They are considered to be some of the oldest rock formations on Earth, such as the Hadaic Acasta Gneiss, which formed about 4,030 million years ago [1External link].

Hornblende gneiss consists mainly of hornblende, a greenish to black mineral that belongs to the amphibole group. The name "hornblende" is derived from the mineral's external resemblance to deer antlers, as well as from medieval miners' language, in which "blende" denoted metallic shiny minerals [4External link]. Hornblende is an important constituent of many metamorphic rocks and occurs as prismatic crystals or fine fibers.

Hornblende gneiss has a characteristic foliated structure due to the parallel arrangement of its mineral constituents during metamorphic alteration. In addition to hornblende, it usually contains feldspar, quartz, and possibly other minerals such as mica or garnet, depending on specific geologic conditions during rock formation.

The exact composition and appearance of hornblende gneiss can vary by geological region. It is a hard rock that can appear in different shades such as greenish, gray, black or reddish. Due to its density and hardness, hornblende gneiss is well suited as a construction material, especially for paving stones, stair treads, flooring and other architectural applications.

Overall, hornblende gneiss is a fascinating metamorphic rock with a rich geological history. Its unique structure and composition make it an important research object for geologists and geoscientists who want to learn more about the formation and evolution of the Earth's crust.

Location of the hornblende gneiss near the village Rothenburg/Kyffhäuser

Image: Thomas Voigt