I am also energy-sensitive, and I understand your fears. You've been given something that you worry may carry a negative intent, and you hold the presumption that this item was infused with "black" magic. This is rather like an acquaintance at work who, after I touched a wound he was showing me, asked if I had "put bad juju on it" - which makes me wonder why his first assumption was that I was doing something bad.
In any case: Metals hold and transfer energy easily, though various metals may have differing properties. Hematite, as noted above, tends to gather energy - particularly darker, heavier, or low-cycle energies. As suggested by the other answers, your own emotional energies may be feeding into this item and coloring its original energy state.
You state that your expertise lies in energy fields. Since charms, curses, spells and other magic(k)s rely on energy fields in the first place, you're working at the deepest level anyway. All you need to do is take hold of the energies within the item, visualise the emotion and spirit toward which you wish to transform those energies, and release your held breath, simultaneously allowing your energies to flow from the heart. Let go of all these these energies at the end of that breath, so that you are no longer in contact and therefore not adding anything else to the working. With the next breath you take, the transformation will be complete.
I would suggest that you focus on a positive relationship with the giver of this gift when you perform the working. Remember that love energy transforms darkness over time; therefore, include love (agape and friendship) with your goal.
Breaking a curse or spell is as simple as snapping your fingers. Take hold of these energies; then, as you snap, visualise the disconnect or disjunction - the cut or crack by which those energies and/or their controlling circuit become broken and stop flowing, soon to dissipate. To simply toss the energies aside, just flick them off with your fingers.
But part of me wonders, since you've been working with spirits, why you didn't just consult with your spirit guides. After all, they ought to know something about this stuff too.