ive collected quite a few of these and was told the recipes in the reactive procs arent possible to make, is this true? what are these used for then?

You can make level 40 potions with them

Ancient pure Mercury = strong Elixir of Speed (17% Self Haste)
Ancient Mirror = strong Elixir of shard Skin (Damage Shield 4,2)
Ancient Lich Tooth = Essence of weariness (increases endurance cost) lvl 50 Poison
Ancient Nerotic Brain Fluid = Essence of Lethargy (degreases attack speed) lvl 50 Poison
Ancient Troll Blood = strong Elixir of mending (health reggen)
Ancient Giant Blood = strong Elixir of Invigoration ( Endurance reggen Buff)
Ancient crushed Focus Stone = strong Elixir of Replenishment ( Power Reggen Buff)

any list of mobs where these drop?

Dont know the other realms, but in Albion mainly the Danoin Soldiers in Lyonesse drop them

Pogmahon wrote:any list of mobs where these drop?

i think this one is right at least for Midgard it is
http://camelot.allakhazam.com/item.html?citem=6963

personally i prefer to farm the Broken Jotuns in Vanern Swamp for those drops