Perditio is the aspect of entropy, destruction, and chaos. It is possibly the most widely-used Primal Aspect, fueling both the Entropic Processing crucible recipes, and the Arcane Bore.
A jar of Perditio will greatly speed the mining of the Arcane Bore, and the essentia is also used for a whole category of crucible recipes, notably the one converting cobblestone via gravel into sand. It also is used in some infusions.
The most common source is cobblestone, but note that better yield can be gotten by first converting the cobblestone into stairs. (The stairs are two-thirds the number of the cobblestone blocks, but each has 2 points instead of 1.) It can also be distilled from Cactus blocks or Gunpowder.
It also can be centrifuged from a number of compounds, many of which may also be available in surplus: Mortuus, and Vacuuos are probably the most common. (Before 4.2.3, Telum was also a source.)