L chondrite
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The L type ordinary chondrites are the second-most common type of meteorite, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites[1].
Their name comes from their relatively (L)ow iron abundance, with respect to the H chondrites, which is about 20-25% by weight. Characteristic is the fayalite content (Fa) in olivine of 21 to 25 mol%. About 4-10% nickel-iron is found as a free metal, making these meteorites magnetic, but not as strongly as the H chondrites.
The most abundant minerals are olivine and hypersthene (an orthopyroxene), as well as nickel-iron metal and troilite. Chromite, Na-rich feldspar and Ca-phosphates occur in minor amounts. Petrologic class 6 dominates, with over 60% of the L chondrites falling into this class. This indicates that the parent body was sizeable enough (>100 km in diameter) to experience strong heating[2].
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 event has been radioisotope dated to around 500 million years ago[3].
The parent body/bodies for this group are not known, but plausible suggestions include 433 Eros and 8 Flora, or the Flora family as a whole. 433 Eros has been found to have a similar spectrum, while circumstantial evidence for the Flora family includes: 1) The Flora family is thought to have formed about 1000 to 500 million years ago; 2) it lies in a region of the asteroid belt that contributes strongly to the meteorite flux at Earth; 3) it consists of S-type asteroids, whose composition is similar to that of chondrite meteorites; 4) The Flora family parent body was over 100 km in diameter.
Historically, the L chondrites have been named hypersthene chondrites or olivine hypersthene chondrites for the dominant minerals, but these terms are now obsolete.
[edit] References
- Natural History Museum, meteorite catalogue
- D. Nesvorný et al The Flora Family: A Case of the Dynamically Dispersed Collisional Swarm?, Icarus, Vol. 157, p. 155 (2002).
- H. Haack et al Meteorite, asteroidal, and theoretical constraints on the 500-Ma disruption of the L chondrite parent body, Icarus, Vol. 119, p. 182 (1996).
- www.meteorite.fr
