I found some of this last night for sale in the Rivervale Cleric's guild. Perhaps sold to the merchant by a player? I don't think it was at the bottom of the inventory. I believe they wanted about 3pp for it, and I was apprehensive to them at the time.
This item randomly drops off any mob level 30 or above. Pretty Rare. It is used in posion for some of the "Berzerker madness" line of posions. Example : 1 Sealed posion Vial + 1 etheral suspenion + 1 Succulent sap (Found in OT) + 2 Of these Crystalized sulfurs makes a 500+ Dmg DoT over 6 ticks with the side effect of raising that mob's str and ac by about 20 for that duration.
I don't think that is the correct recipe for it. The Mortar and Pestle only has 4 slots, and you said 5 items. Two of them are the same and COULD be stacked, but you can only make poisons and most other combines with everything unstacked.
Zyke has the recipe perfectly correct. The mortar and Pestle has 6 slot, not 4, so the five ingredients will fit quite nicely inside for the combine (with room to spare! 8P)