| Subdivision: | Class |
| Mesosiderite | |
| Type: | Stony-iron |
| Composition: | Meteoric iron (kamacite, taenite & tetrataenite); silicates (mostly pyroxene & Ca-rich plagioclase); sulphides (troilite) |
| Number Of Specimens: | 208 |
| Image2 Caption: | Chinguetti mesosiderite |
Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate. They are breccias with an irregular texture; silicates and metal occur often in lumps or pebbles as well as in fine-grained intergrowths. The silicate part contains olivine, pyroxenes, and Ca-rich feldspar and is similar in composition to eucrites and diogenites.[1] [2]
They are a rare type of meteorite; as of November 2014 only 208 are known (of which 56 come from Antarctica) and only 7 of these are observed falls. On the other hand, some mesosiderites are among the largest meteorites known.
At Vaca Muerta in the Atacama Desert in Chile, many fragments with a total mass of 3.8 tons were found in a large strewnfield. They were first discovered in the 19th century by ore prospectors who mistook the shiny metal inclusions for silver and thought they had found an outcrop of a silver ore deposit. Later when an analysis was made and nickel-iron was found, the true nature as a meteorite was established. The meteorite was called Vaca Muerta.[3] The picture at right shows a cut and polished piece of Vaca Muerta.
The most recent fall of a mesosiderite occurred at Dong Ujimqin Qi in China, on September 7, 1995, where three large pieces with a total mass of fell. The fall of the Estherville mesosiderite in Iowa, US occurred on May 10, 1879. After a brilliant fireball had been seen, a shower of several large masses and many small fragments fell, totaling . The fall at Lowicz in Poland on March 12, 1935, yielded many (more than 50) fragments with a total weight of . The other observed mesosiderite falls occurred in 1842 at Barea (Spain), in 1880 at Varamin (Iran), in 1933 at Dyarrl Island (Papua New Guinea), and at Patwar (India) in 1935.[4] The legendary Chinguetti meteorite is also supposed to be a mesosiderite.
The asteroid 16 Psyche is a candidate for the parent body of the mesosiderites.[5] However, a reliable delivery mechanism lacks for Psyche, and spectral analysis indicates the mesosiderites derive from the Maria Asteroid Family [6]