Anorthosite is a calcium-rich igneous rock that is found across the planet and beyond – it is a prominent component of rocks brought back from the moon. Anorthosite is mined in some places, as it may contain large amounts of Labradorite, Titanium, or Aluminum, each of which have significant commercial uses.
Hardness:
6 - 6.5
Density:
2.65 - 2.85 g/cm³
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Properties
Values
Characteristics
Cultural
Common Questions
General Info About Anorthosite
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Physical Properties of Anorthosite
Texture
Phaneritic
Colors
Bluish-grey, black, brown, green, grey, greenish grey, pink, white, etc.
Magnetism
Potentially Magnetic
Grain Size
Coarse grained
Hardness
6 - 6.5 , Hard
Density
2.65 - 2.85 g/cm³, Normal Weight
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Rarity
Uncommon
Economic Value of Anorthosite
The primary economic value of anorthosite bodies is the titanium-bearing oxide ilmenite. However, some Proterozoic anorthosite bodies have large amounts of labradorite, which is quarried for its value as both a gemstone and a building material. Archean anorthosites, because they are aluminium-rich, have large amounts of aluminium substituting for silicon; a few of these bodies are mined as ores of aluminium. Anorthosite was prominently represented in rock samples brought back from the Moon, and is important in investigations of Mars, Venus, and meteorites.
Characteristics of Anorthosite
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Rock Types of Anorthosite
Anorthosite on Earth can be divided into five types:
Archean-age anorthosites
Proterozoic anorthosite (also known as massif or massif-type anorthosite) – the most abundant type of anorthosite on Earth[2]
Layers within Layered Intrusions (e.g., Bushveld and Stillwater intrusions)
Mid-ocean ridge and transform fault anorthosites
Anorthosite xenoliths in other rocks (often granites, kimberlites, or basalts)
Cultural Significance of Anorthosite
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Uses of Anorthosite
Anorthosite has a high aluminum content, and as such the aluminum is mined and used for a variety of purposes ranging from household products like cans, utensils, and electrical conductors to larger industrial uses, including the construction of aircraft.
Distribution of Anorthosite
Proterozoic anorthosites typically occur as extensive stocks or batholiths. The areal extent of anorthosite batholiths ranges from relatively small (dozens or hundreds of square kilometers) to nearly 20,000 km (7,700 sq mi), in the instance of the Nain Plutonic Suite in northern Labrador, Canada. Major occurrences of Proterozoic anorthosite are found in the southwest U.S., the Appalachian Mountains (e.g., the Honeybrook Upland of eastern Pennsylvania), eastern Canada (e.g., the Grenville Province), across southern Scandinavia and eastern Europe. Mapped onto the Pangaean continental configuration of that eon, these occurrences are all contained in a single straight belt, and must all have been emplaced intracratonally. The conditions and constraints of this pattern of origin and distribution are not clear. However, see the Origins section below.
Geochemistry of Anorthosite
Proterozoic anorthosites are typically >90% plagioclase, and the plagioclase composition is commonly between An40 and An60 (40–60% anorthite). This compositional range is intermediate, and is one of the characteristics which distinguish Proterozoic anorthosites from Archean anorthosites (which are typically >An80). Proterozoic anorthosites often have significant mafic components in addition to plagioclase. These phases can include olivine, pyroxene, Fe-Ti oxides, and/or apatite. Mafic minerals in Proterozoic anorthosites have a wide range of composition, but are not generally highly magnesian. The trace-element chemistry of Proterozoic anorthosites, and the associated rock types, has been examined in some detail by researchers with the aim of arriving at a plausible genetic theory. However, there is still little agreement on just what the results mean for anorthosite genesis; see the 'Origins' section below. A very short list of results, including results for rocks thought to be related to Proterozoic anorthosites, Some research has focused on neodymium (Nd) and strontium (Sr) isotopic determinations for anorthosites, particularly for anorthosites of the Nain Plutonic Suite (NPS). Such isotopic determinations are of use in gauging the viability of prospective sources for magmas that gave rise to anorthosites. Some results are detailed below in the 'Origins' section.
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