Anorthosite

Anorthosites (also Plagioklasite ) are leukokrate plutonic rocks, which are characterized by a very high proportion of plagioclase. They often fall through intense iridescent reflections of light on in their crystals.

Mineral content and composition

The determining Plagioklasanteil of more than 90 vol - % is anorthite ( CaAl2Si2O8 (90-100 % anorthite ) ) and similar members of his group, as andesine or labradorite formed. It is a Ca - rich feldspar. The feldspars of the anorthosites are usually large grained and shimmer ever lively on the light. The effect of their spectacular light reflections is also referred to as " labradorisieren ". The scientific term for this phenomenon is Pseudochromasie.

Another mineral constituents occur ortho-and clinopyroxene, olivine and other Mafite as titanomagnetite, almandine and iron and copper sulfides, also on the minerals biotite, corundum and rutile. Some are mineable mineralization.

Depending on Feldspartart a distinction between andesine - anorthosite or labradorite anorthosite. This is the most common distinctive manner in this group of rocks.

After the shares of some accessory mineral contents are also referred to:

• Gabbro - anorthosites; with Mafitgehalten 10 to 22.5 percent
• Noritische anorthosites; Content of orthopyroxene higher than clinopyroxene
• Troktolithische anorthosites, Olivingehalt higher than the Pyroxenanteile.

In addition, two other types are described:

• Two - plagioclase anorthosite; of the feldspars Bytownite and andesine
• Quartz- leading anorthosites; depending on the quartz content, a transition to the tonalite.

Naming and early descriptions

The rock name is derived from the Feldspatart anorthite. An outdated name is Anortholith and was quoted by Thomas Sterry Hunt in 1864.

In the geological exploration of the region around Château -Richer in the Canadian province of Québec Thomas Sterry Hunt examined a crystalline complex with a surface area of about 125 square kilometers. He published his results in 1855 under the title Examinations of some feldspathic rocks (Phil. Mas. , Ser. 4, 9, page 354-363 ) and described so that, according to current terminology, a massif of andesine - anorthosite. Later, there was a renewed exploration by William Edmond Logan in this area.

However, the first scientific description of the rock dates from the year 1863 by Thomas Sterry Hunt and appeared in the work of the Commission géologique Géologie du Canada du Canada under the editorial direction of William Edmond Logan. This occurrence is now known as anorthosite complex or as Grenville - orogen of the Canadian Grenville Province.

Occurrence

Terrestrial occurrence

Anorthosites occur in individual plutons, but much more frequently than tape or location in Gabbrovorkommen.

Significant deposits of the rock can be found in Canada ( in Ottawa ), Ukraine ( at golovinskoye ), Finland ( in Ylämaa and Nuijamaa ) and Norway ( at Sokndal and Hå ).

Extraterrestrial occurrences

The majority of the primary lunar crust, and in particular the high altitudes, consists of anorthosite. As a result of the countless Impacts of particles from space over long periods, however, the upper rock structures have been greatly changed. Reflows and mechanical comminution have received only a few unchanged Anorthositlagen on the lunar surface and changed the original rock structures. This process is referred to as Impaktmetamorphose. With its crystal structure of the local anorthosite contains relatively large amounts of the compatible therewith heavy trace element europium.

Use

Due to the striking visual effects, these rocks are mainly to be found in exclusive interior designs or in the tomb design.

Types of natural stone

• Blue Eyes, (Canada, at Nain )
• Volga Blue (Russian Labrador ), (Ukraine, Zhitomir region )
• Spectrolite, (Finland, Ylämaa )