Hematite
Hematite is the mineral form of iron oxide (Fe2O3). Hematite is magnetic and care needed to be taken when using this element around devices like deflectors because they can be charged with its polar element magnasite which is also magnetic. If the two elements come into contact with one another a feedback pulse could be generated, producing a shock.    

In 2370, Miles O'Brien asked Joseph to have a look at a hematite deposit on Orellius Minor as a reason to distract and incapacitate him. ()

In 2378, while taking off from Ledos, Seven of Nine and Chakotay crashed into an energy barrier. They tried to use the deflector to breach it but a little girl wearing hematite beads got too close and was shocked in the process. ()

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