Eucrite
Encyclopedia
Eucrites are achondritic
stony meteorite
s, many of which originate from the surface of the asteroid
4 Vesta
and as such are part of the HED meteorite
group. They are the most common achondrite group with well over 100 distinct finds at present.
Eucrites consist of basalt
ic rock from the crust
of 4 Vesta
or a similar parent body. They are mostly composed of Ca
-poor pyroxene
, pigeonite
, and Ca
-rich plagioclase
(anorthite
).
Based on differences of chemical composition and features of the component crystals, they are subdivided into several groups:
Eucrite is also a now obsolete term for bytownite
-gabbro
found on Earth. The term was used as a rock type name for some of the Paleogene
igneous rock
s of Scotland
.
Achondrite
An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies...
stony meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s, many of which originate from the surface of the asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
4 Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....
and as such are part of the HED meteorite
HED meteorite
HED meteorites are a subgroup of achondrite meteorites. HED stands for "Howardite–Eucrite–Diogenite".These achondrites came from a differentiated parent body and experienced extensive igneous processing not much different from the magmatic rocks found on Earth and for this reason they closely...
group. They are the most common achondrite group with well over 100 distinct finds at present.
Eucrites consist of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic rock from the crust
Crust
Crust may refer to:* Crust * The Crust, television seriesPhysical sciences:* Crust , at least continent-wide structure* Soil crust, local biology-sensitive structureFood:* Crust, dense surface layer of bread...
of 4 Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....
or a similar parent body. They are mostly composed of Ca
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
-poor pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
, pigeonite
Pigeonite
Pigeonite is a mineral in the clinopyroxene group. It has a general formula of Si2O6. The calcium cation fraction can vary from 5% to 25%, with iron and magnesium making up the rest of the cations....
, and Ca
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
-rich plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
(anorthite
Anorthite
Anorthite is the calcium endmember of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's crust. The formula of pure anorthite is CaAl2Si2O8.-Mineralogy :...
).
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, though not exclusively, regolithRegolithRegolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
brecciaBrecciaBreccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
s 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.
- Main series eucrites formed near the surface and are mostly, though not exclusively, regolith
- Cumulate eucrites are rare types with oriented crystals, thought to have solidified in magma chambers deep within Vesta4 VestaVesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....
's crust. - Polymict eucrites are regolithRegolithRegolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
brecciaBrecciaBreccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
s consisting of mostly eucrite fragments and less than one part in ten of diogeniteDiogeniteDiogenites are a subgroup of the HED meteorite group, a type of achondritic stony meteorites.-Origin and composition:Diogenites originates from deep within the crust of the asteroid 4 Vesta, and as such are part of the HED meteorite group...
, an arbitrary dividing line from the howarditeHowarditeHowardites are achondritic stony meteorites that originate from the surface of the asteroid 4 Vesta, and as such are part of the HED meteorite group. There are about 200 distinct members known.-Characteristics:...
s, which are related in structure. They are comparably rare.
Etymology
Eucrites get their name from the Greek word eukritos 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
Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals. It is usually defined as having "%An" between 70 and 90. Like others of the series, bytownite forms grey to white triclinic crystals commonly exhibiting the typical plagioclase twinning and associated...
-gabbro
Gabbro
Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....
found on Earth. The term was used as a rock type name for some of the Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
igneous rock
Igneous rock
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...
s of Scotland
Geology of Scotland
The geology of Scotland is unusually varied for a country of its size, with a large number of differing geological features. There are three main geographical sub-divisions: the Highlands and Islands is a diverse area which lies to the north and west of the Highland Boundary Fault; the Central...
.
External links
- Eucrite images - Meteorites Australia