Iron Meteorites Iron meteorites are the most easily recognizable meteorites. Sin

Question

Iron Meteorites Iron meteorites are the most easily recognizable meteorites. Since even a casual examination shows that they are not ordinary rocks, they tend to be very common in collections although they are rare in space, comprising only about 5% of all meteorites. They are very dense and except for a thin crust made by the melting of the exterior during their passage through the atmosphere, they look and feel like metal. Chemically they are composed mostly of iron with a few percent nickel and a little cobalt. When sawed in half, polished, and etched with a mild acid, they display a geometrical pattern called a Widmanstätten pattern as in the figure. The pattern is actually crystals of iron and nickel that form as a result of the meteorite having cooled very slowly (about 1°C per 1 million years) under very high pressure. The existence of a Widmanstätten pattern is our best evidence that iron meteorites were once the cores of larger, differentiated bodies. Buried deep in a body, the mass of the overlying rocks provide the high pressure and insulation for slow cooling

Explanation / Answer

Telluric iron, an extremely rare metal not found in many places on Earth, is a metallic iron-nickel alloy (not an ore) which is very similar to meteorites, also displays very coarse Widmanstätten structures. It is similar to meteoritic iron in that it has very coarse Widmanstätten structures which most likely develop through very slow cooling that occurred in Earth’s mantle in crust.

And in the mechanism of producing this pattern, the formation of Ni-poor kamacite proceeds by diffusion of Ni in the solid alloy at temperatures between 700 and 450 °C, and can only take place during very slow cooling, about 100 to 10,000 °C/Myr, with total cooling times of 10 Myr or less.[9] This explains why this structure cannot be reproduced in the laboratory.

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.