Eucrites are achondritic stony

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...

s, many of which originate from the surface of the

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

4 Vesta Vesta (minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, the ...

and are part of the HED meteorite clan. They are the most common achondrite group with over 100 meteorites found. Eucrites consist of basaltic rock from the crust of

or a similar parent body. They are mostly composed of calcium-poor

pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

, pigeonite, and calcium-rich plagioclase (

anorthite Anorthite is the calcium endmember of the plagioclase feldspar mineral series. The chemical formula of pure anorthite is Ca Al2 Si2O8. Anorthite is found in mafic igneous rocks. Anorthite is rare on the Earth but abundant on the Moon. Mineralo ...

). Based on differences of chemical composition and features of the component crystals, they are subdivided into several groups: * Non-cumulate eucrites are the most common variety and can be subdivided further: ** Main series eucrites formed near the surface and are mostly regolith breccias lithified under the pressure of overlying newer deposits. ** Stannern trend eucrites are a rare variety. ** Nuevo Laredo trend eucrites are thought to come from deeper layers of 4 Vesta's crust, and are a transition group towards the cumulate eucrites. * Cumulate eucrites are rare types with oriented crystals, thought to have solidified in magma chambers deep within

's crust. * Polymict eucrites are regolith breccias consisting of mostly eucrite fragments and less than one part in ten of diogenite. They are less common.

Etymology

Eucrites get their name from the Greek word meaning "easily distinguished". This refers to the silicate minerals in them, which can be easily distinguished because of their relatively large grain size. Eucrite is also a now obsolete term for

bytownite Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals with composition between anorthite and labradorite. It is usually defined as having between 70 and 90% An (formula: (Ca0.7-0.9,Na0.3-0.1) l(Al,Si)Si2O ...

- gabbro, an igneous rock formed in the Earth's crust. The term was used as a rock type name for some of the

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

igneous rocks of Scotland.Sutherland, D. S. (1982) ''Igneous Rocks of the British Isles'', Chichester, John Wiley, page 536.

References

External links

Eucrite images
- Meteorites Australia {{Meteorites Planetary science Asteroidal achondrites 4 Vesta it:Meteorite HED#Eucriti

Etymology

See also

References

External links