Stony-Iron Meteorites |
At about 1% of observed falls, stony-iron meteorites are the rarest of the 3 general classes. Most contain about half iron and half silicate minerals. Because of their high iron content making them similar to irons, they are somewhat resistant to weathering and are found more often than they are seen to fall. |
Pallasites: Pallasites are composed of olivine crystals in a matrix of nickel-iron. They are formed at the core-mantle boundry of differentiated asteroids. As the magma in a differentiated asteroid begins to cool, various minerals begin to crystalize out of it and settle to the bottom. Since olivine has the highest melting point of all the minerals in asteroidal magma, it crystalizes first and settles just above the nickle-iron core. The exact mechanism by which the olivine crystals become suspended in the nickle-iron is not understood, but it is probably a combination of pressure from overlying rock, convection currents in the liquid core and shock waves from surface impacts. |
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Brahin, Minsk, Russia Pallasite Found-1810 Slice |
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Imilac, Atacama Desert, Chile Pallasite Found-1822 Whole specimen |
Mesosiderites Mesosiderites are polymict breccias, meaning they are composed of fragments of unrelated rocks. They are made of pieces of nickel-iron metal and silicate rock similar in composition to the eucrite and diogenite achondrites. They are thought to form in differentiated asteroids where the silicate matle and iron core become mixed by impacts with other asteroids. |
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Vaca Muerta, Atacama Desert, Chile Mesosiderite Found-1861 Endpiece |