Daubréelite
Daubréelite is an iron-chromium sulfide that forms thin plates in troilite in iron meteorites and enstatite meteorites.
Daubréelite is a sulfide of iron and chromium, FeCr2S4, named after the nineteenth-century French geologist Gabriel Auguste Daubrée. It is black and opaque.
It is found in meteorites formed with little oxygen, where chromium bonds to sulfur instead of forming the oxide chromite. In iron meteorites it often occurs as thin parallel plates inside troilite nodules, separated out as the sulfide cooled slowly. It is also common in enstatite chondrites and aubrites.
The mineral is a useful indicator of oxygen levels. In ordinary chondrites almost all chromium sits in chromite, but in the highly reduced enstatite meteorites a share of it ends up in daubréelite. Under reflected light on a polished section it appears grey with a slight brown tint, and its plates are a good clue that the host sulfide cooled slowly from a melt deep in an asteroid.
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