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A rare two and a half kilogram meteorite has been discovered by an amateur rock collector on the shores of Lake Huron in Canada. The meteorite was discovered by 78 year old Carl Young whilst he was looking for driftwood along the shore. He realised it was something unusual because it was magnetic and very dense. The rock turned out to be a stony-iron meteorite known as a pallasite that consists of green olivine crystals contained within iron-nickel metal. Pallasites are rare and comprise only 1% of known meteorites.
Pallasites are thought to be samples of asteroids that melted early in their history to form a metallic core and a silicate (stony) mantle. This layered structure is similar to that of the planets and forms because the densest metal liquids sink to the centre of the body and the lightest silicate liquids rise to form a crust. Pallasites are believed to come from the boundary between the metallic core of an asteroid and the stony, olivine-rich overlying mantle and provide us with information on how melted asteroids and planets form.
The mystery of pallasites and iron meteorites, however, is that no olivine-rich melted stony meteorites, which could be part of the overlying mantle of melted asteroids, are known. Likewise although there are many metal (M-type) and metallic-stony (some S-type) asteroids in the main belt, there are very few olivine-rich (A-type) asteroids. One explanation is that after the large melted asteroids were broken up during collisions with other asteroids, early in their history, the fragments from olivine-rich mantle had the highest speeds and were eventually thrown out of our Solar System entirely or collided with the planet Jupiter.
More info: Globe and Mail
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