Akaganeite
Akaganeite is a chlorine-bearing iron oxyhydroxide that causes iron meteorites to crack and weep rust.
Akaganeite is an iron oxyhydroxide containing chlorine in its crystal structure. It was named after the Akagane mine in Japan.
In meteorite collections, akaganeite is the villain. Iron meteorites that have spent time in the ground often absorb chloride from soil water. Once in a collection, the chloride reacts with moisture and the iron to form akaganeite, a process once blamed on a mineral called lawrencite. Akaganeite takes up more space than the metal it replaces, so it pushes open cracks, makes the surface weep orange-brown droplets and can eventually split a specimen.
The cure is prevention: keeping iron meteorites at low humidity, ideally below about 30 to 40 per cent, slows the reaction dramatically. Curators sometimes treat badly affected specimens by soaking out chloride under controlled conditions, but this is specialist work. For home collectors, a sealed box with silica gel is the simplest protection.
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