Stony irons pallasites

Stony irons are nonchondritic meteorites that contain roughly equal proportions of silicate minerals and metal. Two types of stony irons - pallasites and mesosiderites - are distinguished. Pallasites consist of approximately equal amounts of metal and olivine (one small group contains pyroxene as well). Mesosiderates also have approximately equal proportions of metal and silicate, but the silicate fraction is basalt. 

Differentiated (planetary) Achondrites Angrites Aubrites Brachinites HED meteorites Eucrites Howardites Diogenites Ureilites Stony-irons Pallasites... 

The stony-iron meteorites are intermediate between chondrites and irons. These very rare meteorites are equal mixtures of iron/nickel alloys and silicate minerals. Pallasites are striking examples of this type of meteorites, consisting of green olivine crystals in a matrix of metallic iron. Another type of stony-iron meteorite, called mesosiderites, contain pyroxene and plagioclase feldspars, minerals that are common on Earth. 

Figure 10.1 (a) a chondritic meteorite (b) a pallasite stony-iron meteorite (c) an iron meteorite (d) S-type asteroid 243 Ida (e) C-type asteroid 253 Mathilde. Credit NASA. 

Pallasites are stony irons composed of roughly equal amounts of silicate (dominantly olivine), metal, and troilite (Figure 25). There are three separate pallasite types that are distinguished by differences in silicate mineralogy and composition (Table 6), metal, and oxygen isotopic... 

Most CRE ages and histories of pallasites rest shakily on noble gas analyses alone. We summarize the results in Figure 17. Pallasite exposure ages are longer than those of most stony meteorites and comparable to those of the other major stony iron group, the mesosiderites. 

Stony irons. Stony-iron meteorites are those which contain equal proportions of silicate minerals and metallic iron. Pallasites are made up of olivine and Fe-Ni metal and are thought to represent samples from the core-mantle boundary of their parent body. Mesosiderites are brecciated mixtures of silicates and Fe-Ni metal. 

The third large category of meteorites, the stony-iron meteorites, has traditionally been divided into two major groups, the pallasites and the mesosiderites, again based on their chemical composition. The pallasites consist of olivine crystals embedded in matrix of iron-nickel alloy, while the mesosiderites have a complex structure that includes pyroxene, plagioclase, olivine, and other minerals interspersed with an iron-nickel base. Some authorities now recognize a number of other classes of stony-iron meteorites that are different from the pallasites and mesosiderites in the kinds and amounts of minerals present. 

Stony irons aubrites, ureihtes Pallasites, mesosiderites Pallasites derived from core-mantle... 

Meteorites can be classified into stony, stony iron and iron. The most common meteorites are chondrites which are stony. Radiometric dating indicate an age of about 4.5x10 years. Achondrites are also stony but they are considered differentiated or reprocessed matter. They are formed by melting and recrystallization on or within meteorite parent bodies. Pallasites are stony iron meteorites composed of olivine enclosed in metal. 

Stony meteorites are similar to igneous rocks (rocks formed by fire) on earth, but they have less silicon and oxygen, and more iron, cobalt, and trace metals. A third kind of meteorite, called pallasite, is somewhere between the other two types. It is about half iron and half stone, in a mixture not normal on earth. 

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