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 solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...

, 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 differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form pr ...

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 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 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 of this type, making it the secon ...

6 Hebe, with less likely candidates being

3 Juno ) , mp_category=Main belt (Juno clump) , orbit_ref = , epoch= JD 2457000.5 (9 December 2014) , semimajor=2.67070 AU , perihelion=1.98847 AU , aphelion=3.35293 AU , eccentricity=0.25545 , period=4.36463 yr , inclination=12.9817° , asc ...

and

7 Iris Iris (minor planet designation: 7 Iris) is a large main-belt asteroid and perhaps remnant planetesimal orbiting the Sun between Mars and Jupiter. It is the fourth-brightest object in the asteroid belt. It is classified as an S-type asteroid, mea ...

.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). 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 whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun ( perihelion) is less than 1.3 astronomical units (AU) ...

s 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 Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

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 ratios ...

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 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 ...

(an

orthopyroxene The pyroxenes (commonly abbreviated to ''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 calcium (Ca), sodium (Na), iron (Fe I ...

), and

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...

. Characteristic is the

fayalite Fayalite (, commonly abbreviated to Fa) 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 (space group ''Pbnm'') with cell parame ...

(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 whic ...

. 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