H chondrite
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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 the chondrites[1].
The name comes from their (H)igh iron abundance, with respect to other ordinary chondrites, which is about 25-31% by weight. Over half of this is present in a free state, making these meteorites strongly magnetic despite the stony chondritic appearance.
A probable parent body for this group is the S-type asteroid 6 Hebe, with less likely candidates being 3 Juno and 7 Iris[2]. 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.
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.
Historically, the H chondrites have been named bronzite chondrites or olivine bronzite chondrites for the dominant minerals, but these terms are now obsolete.
[edit] References
- Natural History Museum, meteorite catalogue
- M. J. Gaffey & S. L. Gilbert Asteroid 6 Hebe: The probable parent body of the H-Type ordinary chondrites and the IIE iron metorites, Meteoritics & Planetary Science, Vol. 33, p. 1281 (1998).
- www.meteorite.fr
