I have an item call Heart of Darkness. I would like to know what it is used for, what bonuses it offers, and/or anything else (thats relavent).

I think its a Secret Society decoration. So, its not really a real item and has no bonuses,
You can confirm this by using 'eq' and then right after 'eq brief'. The latter should only show real items.
With 'show guilds' and 'show invites' you can probably track down which SS the item is associated to.

It's the secret society guild item for Orion+ if I recall correctly.