Tochilinite
Tochilinite is an unusual layered mineral of iron sulfide and magnesium hydroxide common in CM chondrites.
Tochilinite is a complex mineral made of alternating layers of iron sulfide and magnesium-iron hydroxide. It was first described from terrestrial rocks in Russia in 1971, but it is found in abundance in CM carbonaceous chondrites.
In CMs, tochilinite intergrows with the serpentine mineral cronstedtite to form clumps once known as poorly characterised phases or PCP. These clumps formed during aqueous alteration, as water reacted with metal and sulfide grains inside the parent asteroid. The amount of tochilinite and cronstedtite relative to magnesium-rich serpentine is one measure of how strongly a CM chondrite was altered; heavily altered examples have less of them.
Tochilinite helps define the scale used to sub-classify CM chondrites by their degree of alteration. It breaks down when heated above roughly 250 °C, so its presence also shows that a meteorite was not strongly heated after the water had done its work.
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