The Singing Crystals are unique to Stranglethorn, and are very valuable to certain parties. I can move those crystals, but the cursed Venture Company makes it hard for an honest entrepreneur like myself to gather any!
I'd like to hire you.
The basilisks in Stranglethorn eat the crystal. This gives them their hardened skin, and sometimes decent quality crystal can be harvested from it.
You can get it from any basilisk, but the less nasty ones are along the shores south of Zul'Kunda, to the north.