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.[1] The ordinary chondrites are thought to have originated from three parent asteroids, whose fragments make up the H chondrite, L chondrite and LL chondrite groups respectively.[2]

H chondrite
— Group —
TypeChondrite
Structural classification?
ClassOrdinary chondrite
Subgroups
  • H3
  • H4
  • H5
Parent bodyPossibly 6 Hebe, less likely 3 Juno & 7 Iris
CompositionIron ~25–31%, bronzite (an orthopyroxene), olivine (with characteristic fayalite (Fa) content 16 to 20 mol%), nickel-iron 15–19%, troilite 5%
Petrologic type3 (~2.5%), 5 (40%), 4 & 6 (57.5%)
Alternative namesBronzite chondrites, Olivine bronzite chondrites
Nuevo Mercurio, H5

Name

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The name comes from their High iron abundance, with respect to other ordinary chondrites.

Historically, the H chondrites have been named bronzite chondrites or olivine bronzite chondrites for the dominant minerals, but these terms are now obsolete.

Parent body

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A probable parent body for this group is the S-type asteroid 6 Hebe, with less likely candidates being 3 Juno and 7 Iris.[3] It is supposed that these meteorites arise from impacts onto small near-Earth asteroids broken off from 6 Hebe in the past, rather than originating from 6 Hebe directly.

The H chondrites have very similar trace element abundances and Oxygen isotope ratios to the IIE iron meteorites, making it likely that they both originate from the same parent body.

Iron

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Their high iron abundance is about 25–31% by weight. Over half of this is present in metallic form, making these meteorites strongly magnetic despite the stony chondritic appearance.

Mineralogy

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The most abundant minerals are bronzite (an orthopyroxene), and olivine. Characteristic is the fayalite (Fa) content of the olivine of 16 to 20 mol%. They contain also 15–19% of nickel-iron metal and about 5% of troilite. The majority of these meteorites have been significantly metamorphosed, with over 40% being in petrologic class 5, most of the rest in classes 4 and 6. Only a few (about 2.5%) are of the largely unaltered petrologic class 3.

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See also

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References

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  1. ^ "Natural History Museum, meteorite catalogue". Archived from the original on 2006-05-03. Retrieved 2005-11-29.
  2. ^ NASA (YouTube) – Dr. David Kring – Asteroid Initiative Workshop Cosmic Explorations Speakers Session
  3. ^ M. J. Gaffey & S. L. Gilbert Asteroid 6 Hebe: The probable parent body of the H-Type ordinary chondrites and the IIE iron meteorites, Meteoritics & Planetary Science, Vol. 33, p. 1281 (1998).
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