Primal Fire

Primal Fire is a molten chunk of pure fire goodness. It is used in a wide range of high-end recipes. In addition it is also considered the most in demand, and thus, profitable primal for farming.

Source
Primal Fire is made by combining 10 Mote of Fire, which can be found off fire elementals or in Fel Iron deposits. A guide to finding these can be found here.

Primal fire can also be created through Alchemy with the Transmute: Primal Air to Fire and Transmute: Primal Mana to Fire recipes.

As an ingredient
Primal Fire is used in the following recipes:

Alchemy

 * Major Fire Protection Potion
 * Transmute: Primal Fire to Earth
 * Transmute: Primal Fire to Mana
 * Transmute: Primal Might
 * Transmute: Skyfire Diamond

Blacksmithing

 * Adamantite Breastplate
 * Adamantite Plate Bracers
 * Adamantite Plate Gloves
 * Drakefist Hammer
 * Felsteel Shield Spike
 * Felsteel Whisper Knives
 * Lavaforged Warhammer
 * Ragesteel Breastplate
 * Ragesteel Gloves
 * Ragesteel Helm
 * Red Belt of Battle
 * Red Havoc Boots

Engineering

 * Dimensional Ripper - Area 52
 * Foreman's Reinforced Helmet
 * Gnomish Battle Goggles
 * Gnomish Power Goggles
 * Goblin Rocket Launcher
 * Khorium Power Core

Jewelcrafting

 * Blazing Eternium Band
 * Figurine - Living Ruby Serpent
 * Khorium Inferno Band
 * Pendant of Frozen Flame
 * Pendant of Thawing

Leatherworking

 * Blastguard Belt
 * Blastguard Boots
 * Blastguard Pants
 * Drums of Battle
 * Ebon Netherscale Belt
 * Ebon Netherscale Bracers
 * Ebon Netherscale Breastplate
 * Frost Armor Kit
 * Golden Dragonstrike Breastplate
 * Netherdrake Gloves
 * Netherdrake Helm
 * Stylin' Crimson Hat
 * Windstrike Gloves

Tailoring

 * Belt of Blasting
 * Blackstrike Bracers
 * Flameheart Bracers
 * Flameheart Gloves
 * Flameheart Vest
 * Girdle of Ruination
 * Shadowcloth
 * Spellcloth
 * Spellfire Belt
 * Spellfire Gloves
 * Spellfire Robe

Enchanting

 * Spellpower (bracers enchant)
 * Enchant Cloak - Major Resistance
 * Enchant Shield - Resistance
 * Enchant Weapon - Sunfire

Mining

 * Fire Sunder - creates 10 Motes of Fire