What is anorthosite and what is so special about it?

What is anorthosite and what is so special about it?

Subject: Geography

Section: Physical geography

Context: The lunar surface has ‘Anorthosite’

[a type of intrusive igneous rock] type of soil.

What is anorthosite?

• The term anorthosite was introduced by T.S. Hunt (1863).
• Anorthosites are rocks dominated by plagioclase feldspars..
• Feldspars, together with quartz, are the most common rock forming minerals. The family of feldspars has three “extreme” members:

1. K-containing orthoclase or microcline (KAlSi3O8)
2. Na-containing albite (NaAlSi3O8), and
3. Ca-containing anorthite (CaO·Al2O32SiO2)

• The mixture of albite with anorthite is creating the family of plagioclase feldspars.
• Anorthosites are igneous rocks consisting of 90% or more plagioclase feldspar.
• Categorized into six basic types:

1. Archean megacrystic anorthosites,
2. Proterozoic (massif-type) anorthosites,
3. Anorthosites of layered mafic complexes,
4. Anorthosites of oceanic settings,
5. Anorthosite inclusion in other rock types, and
6. Extra-terrestrial anorthosites.

Where is it found?

• Anorthosites dominate some planetary crusts such as that of the moon and mercury.
• On Earth they are abundant in a few places like:
  • The Grenville Province of the eastern Canadian Shield (Ashwall 2010),
  • In Norway (Scanofennic Shield),
  • In Greenland,
  • In South Africa and
  • In the center of big tectonic plates, where rocks are really old.
  • The two largest anorthosite complexes in Western Europe are situated in Western Norway: the Inner Sogn-Voss province, and the Rogaland province.
• In India, this soil is available in abundance in places like Sithampoondi and Kunnamalai villages surrounding Namakkal, and also in some areas in Andhra Pradesh and northern parts of the country.

Why is it special?

• Anorthosite formula: CaO·Al2O3·2SiO2.
• It contains Aluminium, Silicon and Calcium, minerals which are high in demand.
• Aluminum production from Anorthosite will reduce cost, lessen the procedure and reduce CO2 emissions compared to Bayer’s process of aluminum extraction from Bauxite mineral.