Fill the Empty Water Tube at the Auberdine moonwell, and then investigate the red crystal along Darkshore's eastern mountain wall.
Use this empty vial and fill up on some moonwell water here in Auberdine. Such potent magic should provide a clue as to the composition of the crystal. To do that, you'll pour the liquid over the crystal; it should take care of the rest.
While I don't anticipate anything bad happening to you, I still want you to be careful. Above us to the east is Felwood; if that crystal is tied to that place as I suspect it is, then it could prove to be very dangerous.