"Essences are used both in crafting magical items, as well reagents for spells. Elemental essences are dropped by their respective guardians, and all essences can also be crafted using the essence refiner."
The base essence core is used for crafting and spell creation.(citation needed)
To create a Base Essence Core, you need an Air Essence on the top, Earth Essence on the Bottom, Water Essence on the left, a Fire Essence on the right and some arcane ash in the middle in an essence refiner.