Polygypsum

One of the rarest and most valuable ores in the known universe, Arkonor, has a less well known cousin called Polygypsum. While the two are very similar in chemical composition, the latter is quite unstable, having a tendency to ignite when handled roughly. While posing little danger to a spacecraft, which is built to withstand tremendous heat, this property makes the ore too dangerous under any other circumstances - such as in the business of refining.