Kamacite spindles with schreibersite

Meteorite - Balambala, IIF Iron

Kamacite spindles in iron meteorites, such as the Balambala meteorite, form through a process known as eutectic crystallization. This mechanism is fundamental in metallurgy for alloy production and plays a key role in meteoritics, particularly for iron meteorites. Determining the eutectic "point" where kamacite (a low-nickel Fe-Ni phase) and taenite (a high-nickel Fe-Ni phase) solidify during initial cooling provides critical insights into a meteorite's thermal history.

The interplay between kamacite and taenite, influenced by nickel concentration and cooling rate, can produce elongated, spindle-like kamacite structures within a taenite matrix. These spindles often appear discontinuous, resembling bayonets, and are arranged in an octahedral pattern. In larger examples, schreibersite crystals-a phosphide mineral-form cores within the spindles.

Comparable kamacite spindles are observed in the Ballinoo meteorite, a IIC iron (noted on page 44). However, a key distinction between Ballinoo and Balambala lies in their histories: Ballinoo's spindles show partial recrystallization due to an artificial heating event on Earth. This terrestrial alteration is evident in the modified structure of its kamacite spindles.