Meteorite weathering is the
terrestrial alteration of a
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 ...
. Most meteorites date from the oldest times in the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
and are by far the oldest material available on our planet. Despite their age, they are vulnerable to the terrestrial environment.
Water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
,
chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
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 ...
attack meteorites as soon as they reach the ground.
Weathering scales
In order to quantify the degree of alteration that a meteorite experienced, several qualitative weathering indices have been applied to antarctic and desert samples.
[P. A. Bland, M. E. Zolensky, G. K. Benedix, M. A. Sephton. ']
Weathering of Chondritic Meteorites
''
The most known weathering scale is based upon the effects seen in polished
thin section
In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron ...
s of chondritic meteorites and it ranges from W0 (pristine) to W6 (heavy alteration). It was proposed by Jull A. J. T. et al. (1991) and updated by Wlotzka(1993) and Al-Kathiri et al.(2005).
* W0: no visible
oxidation
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
of metal or
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 ...
, but may be noticeable in transmitted light a limonitic staining. Usually recently
fallen meteorites are of this grade, although some are already W1.
* W1: small oxide rims around metal and troilite, small oxide veins.
* W2: moderate oxidation of metal (about 20-60% replaced).
* W3: heavy oxidation of metal and troilite (60-95% replaced).
* W4: complete oxidation of metal and troilite (>95% replaced), but no alteration of silicates.
* W5: beginning alteration of mafic silicates, mainly along cracks.
* W6: heavy replacement of silicates by clay minerals and oxides.
The Meteorite Working Group at the
Johnson Space Center
The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight in Houston, Texas (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight controller, flight control are conducted. ...
uses weathering categories ''A''
''B'', ''C'' and ''E'' to denote the alteration of
antarctic meteorites.
Their official definitions are:
* A: Minor rustiness; rust haloes on metal particles and rust stains along fractures are minor.
* B: Moderate rustiness; large rust haloes occur on metal particles and rust stains on internal fractures are extensive.
* C: Severe rustiness; metal particles have been mostly stained by rust throughout.
* E: Evaporite minerals visible to the naked eye.
See also
*
Glossary of meteoritics
This is a glossary of terms used in meteoritics, the science of meteorites.
#
* 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites.
* 4 Vesta – second-largest asteroid in the asteroid bel ...
*
Meteorite classification
*
Weathering
Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It occurs '' in situ'' (on-site, with little or no move ...
References
{{Meteorites
Meteorite mineralogy and petrology
Weathering