"Dust of broken heart" is a powdery substance belonging to the Fairies, which is entrusted to Franjean. He wears it in a container attached to a necklace. Rool tries to take some from Franjean to use on a cute girl at a tavern, but in the struggle, he spills it on himself and inadvertantly falls in love with a cat.
Later, Franjean strikes Madmartigan in the nose with the container so that he would stop touching his spear. This causes Madmartigan to temporarily fall in love with Sorsha when he is supposed to be rescuing Elora Danan from her.