Mesosiderites can therefore both record the history of both meteorites and reveal a snapshot of the conditions required for asteroids to melt and form iron cores. In the crash, molten metal mixes together with solid fragments of silicate rocks. Mesosiderites form when debris from a collision between two asteroids is mixed together. The fragments are roughly centimetre-sized and contain a mix of igneous (solidified) silicate and metal clasts (rocks made of pieces of older rocks). Mesosiderite meteorites are breccias, a variety of rock composed of broken fragments of minerals or rock cemented together by a finer material. These types of formations may also be formed by impact melting. However, other scientists think that there are very few olivine-rich meteorites in the asteroid belt, and too many pallasite meteorites for them all to have come from a core-mantle boundary. If this is the case, they could tell us a lot about the formation of Earth and other terrestrial planets. Pallasites are thought to be samples of the boundaries between a metal core and the silicate, olivine-rich mantle around it. Some scientists believe they formed in melted asteroids in a similar way to iron meteorites, where dense iron metal sinks toward the centre to form an iron core. The scientific jury is still out on exactly how pallasite meteorites formed. Elsewhere it can create a pattern of veins through solid metal. Sometimes the olivine does not occur as a single crystal but as a cluster. ![]() Pallasites contain big, beautiful olive-green crystals - a form of magnesium-iron silicate called olivine - embedded entirely in metal.
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