The L type

ordinary chondrite The ordinary chondrites (sometimes called the O chondrites) are a class of stony chondritic meteorites. They are by far the most numerous group, comprising 87% of all finds. Hence, they have been dubbed "ordinary". The ordinary chondrites are t ...

s are the second most common group of

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 moon. When the original object ...

s, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the

H chondrite The H type ordinary chondrites are the most common type of meteorite, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of all chondrites. The ordinary chondrites are thought to have originated from ...

, L chondrite and

LL chondrite The LL chondrites are a group of stony meteorites, the least abundant group of the ordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls (see meteorite fall statistics). The ordi ...

groups respectively.

Name

Their name comes from their relatively low iron abundance, with respect to the

s, which are about 20–25% iron by weight. Historically, the L chondrites have been named ''hypersthene chondrites'' or ''olivine hypersthene chondrites'' for the dominant minerals, but these terms are now obsolete.

Chemical composition

Characteristic is the

fayalite Fayalite (, commonly abbreviated to Fa) is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group ''Pbnm'') with cell parame ...

content (Fa) in olivine of 21 to 25 mol%. About 4–10% iron–nickel is found as a free metal, making these meteorites magnetic, but not as strongly as the

Mineralogy

The most abundant minerals are

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

and

hypersthene Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have f ...

(an

orthopyroxene 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 I ...

), as well as iron–nickel and

troilite Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron-rich endmember of the pyrrhotite group. Pyrrhotite has the formula Fe(1-x)S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency whic ...

Chromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can ...

, sodium-rich

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...

and calcium

phosphates In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

occur in minor amounts.

Petrologic type A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primi ...

6 dominates, with over 60% of the L chondrites falling into this class. This indicates that the parent body was sizeable enough (greater than in diameter) to experience strong heating.

Ordovician meteor event

Many of the L chondrite meteors may have their origin in the Ordovician meteor event, radioisotope dated with uranium-lead at around 467.50±0.28 million years ago. Compared to other chondrites, a large proportion of the L chondrites have been heavily shocked, which is taken to imply that the parent body was catastrophically disrupted by a large impact. This impact has been dated via cosmic ray exposure at around 468.0±0.3 million years ago. Earlier argon dating placed the event at around 470±6 million years ago.Korochantseva et al
"L-chondrite asteroid breakup tied to Ordovician meteorite shower by multiple isochron 40Ar-39Ar dating"

Meteoritics & Planetary Science ''Meteoritics & Planetary Science'' is a monthly peer-reviewed scientific journal published by Wiley-Blackwell on behalf of the Meteoritical Society. It specialises in the fields of meteoritics and planetary science. The journal was established as ...

42, 1, pp. 3-150, Jan. 2007.

Parent body

The parent body/bodies for this group are not known, but plausible suggestions include

433 Eros Eros (minor planet designation: (433) Eros), provisional designation is a stony asteroid of the Amor group and the first discovered and second-largest near-Earth object with an elongated shape and a mean diameter of approximately . Vis ...

and 8 Flora, or the

Flora family The Flora family (''adj. Florian''; ; also known as ''Ariadne family'') is a prominent family of stony asteroids located in the inner region of the asteroid belt. It is one of the largest families with more than 13,000 known members, or approxi ...

as a whole. 433 Eros has been found to have a similar spectrum, while several pieces of circumstantial evidence for the Flora family exist: (1) the Flora family is thought to have formed about 1,000 to 500 million years ago; (2) the Flora family lies in a region of the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, c ...

that contributes strongly to the meteorite flux at Earth; (3) the Flora family consists of

S-type asteroid S-type asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the secon ...

s, whose composition is similar to that of

chondrite A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form pr ...

meteorites; and (4) the Flora family parent body was over in diameter.

References

External links

The Catalogue of Meteorites
{{Meteorites fi:L-kondriitti