The technical name is white phosphorus. Theorically, it should only be used in the dark, in order to enlight enemy targets . In reality, it has been used as a chemical weapon in the iraqi city of Falluja. And not only against combatants and guerrillas, but against unarmed civilians.
The US troops may have become responsible of a massacre with nonconventional weapons, which is what former dictator Saddam Hussein is accused of.

A reportage on this hidden massacre has been broadcasted by RAI News on November 8th to (on the satellite Hot Bird, channel 506 of Sky and RAI 3).
Downloading from Internet here (in Italian only).
This news was published a month ago also by Manifesto: according to the reportage, also Luciana Sgrena and Enzo Baldoni (two italian journalists) were looking for informations on this affair, as they were kidnapped.
The dangerousness of white phosphorus is recognized since 100 years. Unfortunately at that time already, the prohibition, much rigorous for the European countries (artt. 1 and 2), was not applied to the colonies (art.3).
There are terrible images on Internet, than can be found through Google images, typing white phosphorus falluja. I cannot know if they are authentic or at least plausible. For sure, they are terrifying.
Sooner or later, we will have to return to considering depleted uranium, too.

Update November 9th:
US Defense Ministry officer has denied these allegations, afferming the immorality of the use of chemical weapons.