Tonk meteorite
{{Short description|Carbonaceous chondrite meteorite}}
{{Use dmy dates|date=May 2022}}
{{Use Indian English|date=May 2022}}
{{Infobox meteorite
|Name= Tonk
|Image=
|Image_caption=
|Type= Chondrite
|Class= Carbonaceous chondrite
|Group= CI1
|Structural_classification=
|Composition=
|Shock=
|Weathering=
|Country= India
|Region= Rajasthan
|Lat_Long= {{coord|24|39|N|76|52|E|display=inline,title}}{{metbull|24026|Tonk}}
|Observed_fall= Yes
|Fall_date= 22 January 1911
|Found_date=
|TKW= {{convert|7.7|g|oz|abbr=on}}
|Image2= Météorite Alais, exposition Météorites, Muséum national d'histoire naturelle de Paris.jpg
|Image2_caption= The similar Alais meteorite in 2018
}}
Tonk is a small carbonaceous chondrite meteorite that fell near Tonk, India in 1911. Despite its small size, it is often included in studies due to its compositional similarity to the early solar system.
Composition and classification
The meteorite consists of fragments that together weigh {{convert|7.7|g|oz|abbr=on}} and fell near the city of Tonk in India near midday on 22 January 1911.{{cite journal | last=Christie | first=W. A. K. | year=1914 | title=The composition of the Tonk Meteorite | journal=The Journal of the Astronomical Society of India | volume=4 | number=2 | pages=71–72}} It is one of five known meteorites belonging to the CI chondrite group.{{cite journal | last=Mason | first=Brian | title=The Carbonaceous Chondrites | journal=Space Science Reviews | year=1963 | volume=1 | number=4 | pages=621–646 | doi=10.1007/BF00212446 | bibcode=1963SSRv....1..621M | s2cid=121308917 }} This group is remarkable for having an elemental distribution that has the strongest similarity to that of the solar nebula. Except for certain volatile elements, like carbon, hydrogen, oxygen, nitrogen and the noble gases, which are not present in the meteorite, the ratios of the elements are very similar.{{cite journal | last1=Endress | first1=Magnus | last2=Spettel | first2=Bernhard | last3=Bischoff | first3=Adolf | year=1994 | title=Chemistry, petrography, and mineralogy of the Tonk CI chondrite: Preliminary results | journal=Meteoritics | volume=29 | number=4 | pages=462–463| bibcode=1994Metic..29..462E }} Notably though, the meteor is highly enriched in volatile mercury which is undetectable in the solar photosphere, and this is a major driver of the "mercury paradox" that mercury abundances in meteors do not follow its volatile nature and isotopic ratios based expected behaviour in the solar nebula.{{cite journal | last1=Lauretta | first1=D.S. | last2=Devouard | first2=B. | last3=Buseck | first3=P.R. | year=1999 | title=The cosmochemical behavior of mercury | journal=Earth and Planetary Science Letters | volume=171 | issue=1 | pages=35–47| doi=10.1016/S0012-821X(99)00129-6 | bibcode=1999E&PSL.171...35L }}{{cite journal | last1=Meier | first1=M.M.M. | last2=Cloquet | first2=C. | last3=Marty | first3=B. | year=2015 | title=Mercury (Hg) in meteorites: Variations in abundance, thermal release profile, mass-dependent and mass-independent isotopic fractionation | journal=Geochimica et Cosmochimica Acta | volume=182 | pages=55–72| doi=10.1016/j.gca.2016.03.007 | doi-access=free | arxiv=1603.01968 }} These features mean that it is often, despite its small size, included in meteorological studies. The meteorite contains dolomite, magnesite, magnetite, pentlandite and pyrrhotite.