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Pallasite
The pallasites are a Meteorite classification#Terminology, class of stony–iron meteorite. They are relatively rare, and can be distinguished by the presence of large olivine crystal inclusions in the ferro-nickel matrix. These crystals represent mantle and core material from planetary differentiation, differentiated planetesimals, which were destroyed by violent collisions during the early formation of the Solar System. Structure and composition It consists of centimetre-sized olivine crystals of peridot quality in an iron-nickel Matrix (geology), matrix. Coarser metal areas develop Widmanstätten patterns upon etching. Minor constituents are schreibersite, troilite, chromite, pyroxenes, and phosphates (whitlockite, stanfieldite, farringtonite, and merrillite). Classification and subgroups Using the oxygen isotopic composition, meteoric iron composition and silicate composition pallasites are divided into 4 subgroups:O. Richard Norton. ''The Cambridge encyclopedia of meteori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexahedrite
Hexahedrites are a structural class of iron meteorite. They are composed almost exclusively of the nickel–iron alloy kamacite and are lower in nickel content than the octahedrites. The nickel concentration in hexahedrites is always below 5.8% and only rarely below 5.3%. The name comes from the cubic (i.e. ''hexahedron'') structure of the kamacite crystal. After etching, hexahedrites do not display a Widmanstätten pattern, but they often do show Neumann lines: parallel lines that cross each other at various angles, and are indicative of impact shock on the parent body. These lines are named after politician who discovered them in 1848. Chemical classification Concentrations of trace elements (germanium, gallium and iridium) are used to separate the iron meteorites into chemical classes, which correspond to separate asteroid parent bodies. Chemical classes that include hexahedrites are: * IIAB meteorites (includes also some octahedrite Octahedrites are the most common ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ataxite
Ataxites (from Greek meaning "without structure") are a structural class of iron meteorites with a high nickel content and show no Widmanstätten patterns upon etching. Characteristics Ataxites are composed mainly of meteoric iron, a native metal found in meteorites that consists of the mineral taenite with minor amounts of plessite, troilite, and microscopic lamellae of kamacite. Ataxites are the most nickel-rich meteorites known; they usually contain over 18% nickel. The high nickel content is the reason that they do not develop a Widmanstätten structure, because in this case kamacite can be exsolved from taenite only at such a low temperature (below about 600°C) where diffusion is already too slow.F. Heide, F. Wlotzka, Meteorites, Messengers from Space, Springer-Verlag 1995, page 143 Classification Most ataxites belong to the[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pallasite Meteorite
The pallasites are a class of stony–iron meteorite. They are relatively rare, and can be distinguished by the presence of large olivine crystal inclusions in the ferro-nickel matrix. These crystals represent mantle and core material from differentiated planetesimals, which were destroyed by violent collisions during the early formation of the Solar System. Structure and composition It consists of centimetre-sized olivine crystals of peridot quality in an iron-nickel matrix. Coarser metal areas develop Widmanstätten patterns upon etching. Minor constituents are schreibersite, troilite, chromite, pyroxenes, and phosphates (whitlockite, stanfieldite, farringtonite, and merrillite). Classification and subgroups Using the oxygen isotopic composition, meteoric iron composition and silicate composition pallasites are divided into 4 subgroups:O. Richard Norton. ''The Cambridge encyclopedia of meteorites''. Cambridge, Cambridge University Press, 2002. . * Main group pallasites (PMG ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
