ToME: the Tales of Maj'Eyal

Hello guys, I've got a question.

What does "Latent Damage Type: Fire" mod do ?
Found it on three items (Petrified Wood, Runed Skull and some demon gem which provided -50% healing mod when carried, its latent damage type was darkness I believe).

that's for if you socket them in Tirakis Maul or use them as Alchemist bomb ammo

No, its for the Maul and for modifying golem damage.