Anorthosite is a coarse-grained, light-coloured containing rich elements of plutonic rock. It is mainly composed of plagioclase (generally bytownite or labradorite) also sometimes with small amounts of pyroxene. Mineral elements like amphibole, ilmenite, magnetite, olivine, pyroxene and spinel are the mafic minerals also often present. Anorthosite is a phaneritic type of intrusive igneous rock featured by a predominance of plagioclase feldspar (90-100%) and a nominal mafic component (0-10%).
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Anorthosite Chemical Formula
The chemical formula of a real anorthite mineral is CaAl2Si2O8.
Anorthosite is quite significant and commonly used in academic and economic fields.
Anorthosite mineral composition is as follows:
Anorthosite mainly contains plagioclase with 90-100% component in the andesine-labradorite range.
Mafic minerals never cross beyond 10% of the rock.
Some of the plagioclase is overly dense and flourished by later crystallization of ilmenite magnetite, plagioclase or pyroxene forming massive poikilitic grains.
Anorthosite is coarse-grained, leucocratic and hypidiomorphic. Some crystals are in the form of euhedral, while some have imperfectly developed faces and others contain no crystal form at all.
Classification of Anorthosite
Age of the formation (According to the age of the formation of rock, they are categorized as Archean anorthosite and Proteroic anorthosite.)
Occurrence and association (According to the occurrence, they are categorized as Lunar, Layered and Massif anorthosite.)
IUGS (International Union of Geological Society)
They are deposed during the Archean era and are reflected by the high composition of An 85-100 calcic plagioclase. Chemically, calcic anorthosites layers are high in Al2O3 and are typically surrounded by a fine-grained mafic.
They occur during the Proterozoic era creating stocks of batholith size plutons. Apparently, they are restrained to high-grade metamorphism terrains of the Precambrian age.
Likely to form with the primitive lunar crust by crystallization of An-rich plagioclase, a lunar anorthosite has highly calcic plagioclase with lesser olivine, orthopyroxene, and spinel (Mg-Al). They are fine-grained, light-coloured, and quite close to 100% Ca-content.
Anorthosite Moon Rock
From the Earth's surface, the lunar anorthosite is seen as the light-coloured, highly reflective element of the Moon's surface referred to as the lunar highlands. These are actually the Moon's oldest rocks—over 4 billion years old—and enveloped the young Moon's whole surface before its crust was pummeled and fragmented by comets and asteroids.
When we talk about when a type of rock is anorthosite moon then it is a flat, dark commonly circular regions referred to as lunar maria (singular form: mare) are made up of the rock basalt. This basalt specimen was gathered near the rim of Hadley Rille. The fine-grained crystallinity and huge holes imply that this rock crystallized in the neighbourhood of the top of a molten lava flow.
Anorthosite, the designated grey rock well acquainted to hikers and climbers in the Adirondacks is an antiquated type of granite that occurred 15 miles underneath the surface over a billion years ago. Forced to the surface by recent mountain constructing activity, its deep cracks brought into being the valleys and deep lakes of the area.
Anorthosite Thin Section
This rock is a type of highland anorthosite, supposedly a cumulate that occurred as a component of the early lunar crust. This rock consists of plagioclase (~98%) of An95 to An97 and is truly a lithified anorthosite breccia or cataclasite.
The term anorthosite is derived from French ‘anorthose’ (referring to french—plagioclase) was coined by Sterry Hunt.
Though Anorthite is typically rare on the Earth, it is abundant on the Moon.
Anorthosite minerals are not specifically abundant on Earth besides a few places such as the Grenville Province of the eastern Canadian Shield.
As a rock type, anorthosites have occurred over the entire range of geological time, and are expectedly still forming today.
Anorthosite formations are very diverse, and when their distinctive characteristics are used to classify them, it becomes evident that some types show very clear temporal restrictions.
Lunar anorthosite plays a significant part in the investigation of Venus, Mars and meteorites. They also possess the quality of a gem rock.