Metal Grains in Chondritic Meteorites

Abstract

THE nickel–iron minerals taenite and kamacite in octahedrites (iron meteorites) are inhomogeneous, as shown in Fig. 1: taenite crystals are richest in nickel and kamacite crystals are poorest in nickel at the phase boundaries where they abut one another^1–3. This is a natural consequence of the behaviour of nickel–iron alloy systems if they are cooled slowly and steadily, as in the interior of a planet^4–10. The binary nickel–iron phase diagram predicts that beneath ∼ 800° C, as temperature falls, taenite and kamacite should continuously react with one another and change in composition. Nickel concentration should increase steadily in taenite, while in kamacite at T < ∼ 500° C it should decrease.