When used as a focus for healing, however, the crystal greatly reduces the difficulty of the healing effort. An unattuned or borrowed healing crystal reduces the difficulty by two, while an attuned crystal lowers the difficulty by three
Crystals are a natural focus for healing (-1 difficulty).
Using an exclusive focus (that is, it is a focus for one thing only) reduces
the difficulty by one.
Using an item attuned to a person reduces the
difficulty by one.
The attunement process creates a link between the crystal and the healer. While this link makes the crystal more effective as a healing focus, it can also leave the healer more vulnerable to magical attack, should the crystal fall into unfriendly hands.