The Alius in its raw form

The Alius is a chemical mixture of the magical particles on Cortus and the magical particles on Procidens. The mixture was catalyzed, when Spatium accidentally reached Cortus and opened a short-lasting rift between Cortus and Procidens. 

Upon reaching Cortus, The Sacers began a long-lasting operation to contain the mixture within a mountain-cliff, effectively turning it from a gas-like substance, to a physical, solid form of mass. 

Attempting to hasten the birth of their fetuses with the alius, the sacers accidentally created the Humans. Having a small percentage of the alius within them, humans were the only race capable of using the alius similarily to how normal magical particles work.