Heartstones

The Hearstones are magical objects that have fascinated mystics and sorcerers. These stones are major sources of magical power and are thought to have been formed during The Convergence  .
Heartstones are found in dense veins of Dragon Ore , leading to the belief that their origins are similar to that of the Dragons themselves, although this is only a theory. Heartstones are rare enough that to obtain or possess one would be a great notice by any practitioners of magic which causes dragon ore mining to be carefully monitored.
Heartstones can be attuned to by mages in order to tap into their true capabilities. Each stone has a "personality" that can hinder or help the mage attempting to use it.
The first and most common method of use is as a focus for spell casting. By channeling magical energy through the stone, a mages spells are amplified, but run the risk of also being slightly modified based on the stone's personality.
The second use is to bring a very powerful creature or golem to life. The Stone essentially acts as a heart and mind of the animated creation and is directly influenced by the stone's personality. The stone is still not truly sentient, however and without direction will very rarely do much without provocation or direction from its controlling mage. The stone also modifies the construct based on its nature. 
Only a few heartstones are known to have been destroyed, as like the ore they are found in, they are incredibly resilient. When one is destroyed, it shatters in a magical explosion that decimates the surrounding area. Usually such careless action that risks such destruction are generally avoided by mages as they neither want to waste such a valuable object but they also tend to realize they are close enough to the stone to be destroyed themselves in such an event.

Item type

Magical

Rarity

Heartstones are incredibly rare and highly sought after. The only publicly known stone is held by the First Mages College of Zentru . It is at the heart of their Citadel plugged into a construct originally designed by Krato, the First Mage .

In Game

Heart stones are unique magical artifacts that when used as a focus for spells increase the potency of the spell (system dependent).
If used to power a construct, the construct has a minor intelligence with the nature of the stone: Aggressive, Defensive, Feral, or Inert

• Aggressive

  An aggressive stone causes the construct to be prone to violence. - Add a bonus to the constructs initiative checks. While attuned, the construct is only held on a leash and will eagerly attack anything the caster points it at.

• Defensive

  A defensive stone causes the construct to only respond aggressively to perceived threats and will only attack in response to a threat. - Increase the construct's defensive value (AC, Soak, etc. Whatever your RPG system uses). When attuned the construct will resist moving away from the caster out of defensive instinct.

• Feral

  Feral stones are erratic and difficult to control. These stones do not listen to the caster as easily and must be attuned in order to fully control. - If unattuned, the construct gets a free action at the beginning of its combat turn (Bonus action, free action, maneuver, etc.). If attuned, the construct can increase the range band it can move in a single maneuver by one.

• Inert

  Inert Stones do not have the same tendencies of the other types. In fact they follow all instructions without needing to be attuned but they will not perform any tasks unless told to do so.

Stones can be attuned to by spending one hour meditating with the stone. By using a maneuver, one can command the stone to do a direct action while powering a construct/golem.