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Meteorite weathering is the terrestrial alteration of a
Weathering of Chondritic Meteorites
'' The most known weathering scale is based upon the effects seen in polished
Meteorite weathering is the terrestrial alteration of a 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 ...
. Most meteorites date from the oldest times in the Solar System
The Solar System Capitalization 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 "Solar ...
and are by far the oldest material available on our planet. Despite their age, they are vulnerable to the terrestrial environment. Water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
, chlorine
Chlorine is a chemical element with the 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 them. Chlorine i ...
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 ...
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, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
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 whic ...
, 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 (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight control are conducted. It was renamed in honor of the late ...
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 b ...
* 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, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...
References
{{Meteorites Meteorite mineralogy and petrology