H chondrite
Encyclopedia
The H type ordinary chondrite
s are the most common type of meteorite
, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of the chondrite
s.
The name comes from their High iron abundance, with respect to other ordinary chondrite
s, which 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.
A probable parent body for this group is the S-type asteroid
6 Hebe
, with less likely candidates being 3 Juno
and 7 Iris
. 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 meteorite
s, 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.
Ordinary chondrite
The Ordinary chondrites are a class of stony chondritic meteorites. They are by far the most numerous group and comprise about 87% of all finds...
s are the most common type of meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of the chondrite
Chondrite
Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...
s.
The name comes from their High iron abundance, with respect to other ordinary chondrite
Ordinary chondrite
The Ordinary chondrites are a class of stony chondritic meteorites. They are by far the most numerous group and comprise about 87% of all finds...
s, which 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.
A probable parent body for this group is the S-type asteroid
S-type asteroid
S-type asteroids are of a stony composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the C-type.-Characteristics:...
6 Hebe
6 Hebe
6 Hebe is a large main-belt asteroid, containing around half a percent of the mass of the belt. Its apparently high bulk density , however, means that by volume it does not rank among the top twenty asteroids...
, with less likely candidates being 3 Juno
3 Juno
Juno , formal designation 3 Juno in the Minor Planet Center catalogue system, was the third asteroid to be discovered and is one of the larger main-belt asteroids, being one of the two largest stony asteroids, along with 15 Eunomia. Juno is estimated to contain 1% of the total mass of the asteroid...
and 7 Iris
7 Iris
7 Iris is a large main-belt asteroid. Among the S-type asteroids, it ranks fifth in geometric mean diameter after Eunomia, Juno, Amphitrite and Herculina....
. It is supposed that these meteorites arise from impacts onto small near-earth asteroids broken off from 6 Hebe
6 Hebe
6 Hebe is a large main-belt asteroid, containing around half a percent of the mass of the belt. Its apparently high bulk density , however, means that by volume it does not rank among the top twenty asteroids...
in the past, rather than originating from 6 Hebe directly.
The H chondrites have very similar trace element abundances and Oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
isotope ratios to the IIE iron meteorite
IIE iron meteorite
The iron meteorites of the IIE chemical type are octahedrites of various coarseness, most of which contain numerous inclusions of recrystallized stony silicates....
s, making it likely that they both originate from the same parent body.
The most abundant minerals are bronzite
Bronzite
Bronzite is a member of the orthopyroxene group of minerals, belonging with enstatite and hypersthene to the orthorhombic series of the group...
(an orthopyroxene), and olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
. Characteristic is the fayalite
Fayalite
Fayalite 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 with cell parameters a 4.82 Å, b 10.48 Å and c Å 6.09.Iron rich olivine is a relatively common constituent of acidic and...
(Fa) content of the olivine of 16 to 20 mol%. They contain also 15-19% of nickel-iron metal and about 5% of troilite
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 FeS which is iron deficient...
. The majority of these meteorites have been significantly metamorphosed
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
, 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.