- Can be chosen as a burial gift at the beginning of the game.
- Undead Settlement
- Smouldering Lake
- Dropped by Writhing Rotten Flesh.
Fire Gems can be used to infuse a weapon with an essence of fire, which will cause a weapon to inflict equally-split physical and fire damage.
Many Undead enemies or creatures, such as Peasant Hollows and Starved Hounds, are naturally weak to fire damage, and thus, a fire-infused weapon can prove useful. However, one must be cautious, as attacking an enemy with such a weapon now has to take into account two defenses. As such, enemies that possess a resistance to fire will take notably less damage.
Fire infusions also remove all scaling effects present on the weapon after infusion, much like a Deep Gem does, which means in order to achieve maximum damage on deep weapons, the player will have to fully-reinforce one.