The H type

ordinary chondrite The ordinary chondrites (sometimes called the O chondrites) are a class of stony chondritic meteorites. They are by far the most numerous group, comprising 87% of all finds. Hence, they have been dubbed "ordinary". The ordinary chondrites are t ...

s are the most common type of

meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...

, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of all

chondrite A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or planetary differentiation, differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar Syste ...

s. The ordinary chondrites are thought to have originated from three parent asteroids, whose fragments make up the H chondrite,

L 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. The ordinary chondrites are thought to have originated from three parent a ...

and

LL chondrite LL may refer to: * Ll or ll, a digraph that occurs in several natural languages Arts and entertainment *LL, the production code for the 1967 ''Doctor Who'' serial ''The Evil of the Daleks'' * ''Labyrinth Lord'', a fantasy role-playing game * ''L ...

groups respectively.

Name

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

s. 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

A probable parent body for this group is the

S-type asteroid S-type (stony-type or silicaceous-type) asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are ...

6 Hebe 6 Hebe () is a large main-belt asteroid, containing around 0.5% of the mass of the belt. However, due to its apparently high bulk density (greater than that of the Moon), Hebe does not rank among the top twenty asteroids by volume. This high bu ...

, with less likely candidates being

3 Juno Juno (minor-planet designation: 3 Juno) is a large asteroid in the asteroid belt. Juno was the third asteroid discovered, in 1804, by German astronomer Karl Harding. It is tied with three other asteroids as the thirteenth largest asteroid, and ...

and

7 Iris 7 Iris is a large main-belt asteroid and possible remnant planetesimal orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. 7 Iris is classified as an S-type asteroid, meaning that it has a stony co ...

.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 ''Meteoritics & Planetary Science'' is a monthly peer-reviewed scientific journal published by Wiley-Blackwell on behalf of the Meteoritical Society. It specialises in the fields of meteoritics and planetary science. The journal was established a ...

, Vol. 33, p. 1281 (1998). It is supposed that these meteorites arise from impacts onto small

near-Earth asteroid A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun (perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit aro ...

s broken off from

in the past, rather than originating from 6 Hebe directly. The H chondrites have very similar trace element abundances and

Oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

isotope ratios to the

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. Composition and origin They have mineral compositions and oxygen isotope Isot ...

s, making it likely that they both originate from the same parent body.

Iron

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 A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primiti ...

appearance.

Mineralogy

The most abundant minerals are

bronzite Bronzite is a member of the pyroxene group of minerals, belonging with enstatite and hypersthene to the orthorhombic series of the group. Rather than a distinct species, it is really a ferriferous variety of enstatite, which owing to partial alt ...

(an

orthopyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron (Fe( ...

), and

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

. Characteristic is the

fayalite Fayalite (, commonly abbreviated to Fa) is the iron-rich endmember, end-member of the olivine solid solution, solid-solution series. In common with all minerals in the olivine, olivine group, fayalite crystallizes in the orthorhombic system (spac ...

(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 () 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 Fe(1−x)S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency ...

. The majority of these meteorites have been significantly

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

, 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.

Gallery

File:GaoGuenieMeteorite.jpg, Gao-Guenie, H5 File:Chondrite H5.JPG, H5 Dar Bou Nali South Morocco

References

External links

The Catalogue of Meteorites
{{DEFAULTSORT:H Chondrite fi:H-kondriitti