L chondrite

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L chondrite
— Group —
NWA869Meteorite.jpg
NWA 869, an L4-6 chondrite
Type Chondrite
Structural classification ?
Class Ordinary chondrite
Subgroups
  • L3
  • etc
Parent body Possibly 433 Eros, 8 Flora or the Flora family as a whole
Composition Olivine (characteristic fayalite (Fa) of 21 to 25 mol%), hypersthene (an orthopyroxene), nickel-iron 4–10%, troilite, chromite, Na-rich feldspar, Ca-phosphates
Petrologic type 6 (>60%)
Alternative names L chondrite meteorites, Hypersthene chondrites, Olivine hypersthene chondrites
Walters meteorite.jpg
Walters, an L6 chondrite

The L type ordinary chondrites are the second most common group of meteorites, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites.[1] The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively.[2]

Name[edit]

Their name comes from their relatively low iron abundance, with respect to the H chondrites, 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[edit]

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.[citation needed]

Mineralogy[edit]

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 type 6 dominates, with over 60% of the L chondrites falling into this class. This indicates that the parent body was sizeable enough (greater than 100 kilometres (62 mi) in diameter) to experience strong heating.[3]

Ordovician meteor event[edit]

Many of the L chondrite meteors may have their origin in the Ordovician meteor event. 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 470±6 million years ago.[4][5]

Parent body[edit]

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 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 that contributes strongly to the meteorite flux at Earth; (3) the Flora family consists of S-type asteroids, whose composition is similar to that of chondrite meteorites; and (4) the Flora family parent body was over 100 kilometres (62 mi) in diameter.[citation needed]

See also[edit]

References[edit]

  1. ^ Natural History Museum, meteorite catalogue
  2. ^ NASA (YouTube) – Dr. David Kring – Asteroid Initiative Workshop Cosmic Explorations Speakers Session
  3. ^ D. Nesvorný et al. The Flora Family: A Case of the Dynamically Dispersed Collisional Swarm?, Icarus, Vol. 157, p. 155 (2002).
  4. ^ 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).
  5. ^ Korochantseva et al. "L-chondrite asteroid breakup tied to Ordovician meteorite shower by multiple isochron 40Ar-39Ar dating" Meteoritics & Planetary Science 42, 1, pp. 3-150, Jan. 2007.

External links[edit]