Mana cannot fuel a ritual; it lacks the density of power needed to create the effects of a ritual, and disperses into the atmosphere too quickly to be used in one. Aether, however, is a perfect energy source for magical rituals, provided it is condensed into a small package (such as an Aether Crystal) and then steadily released into the ritual’s workings. This makes Aether Crystals a vital resource, as they are by far the most reliable means of powering rituals known to mortalkind.
Every ritualist taking part in a ritual can consume one or more Aether Crystals to power it. Each Aether Crystal consumed this way contributes +1 Ritual Power to the ritual, which is doubled if the mage in question has Mastered that ritual. (Players often refer to the act of consuming Aether Crystals for power as “crushing” them, e.g. “I can crush 4 crystals to help you power that ritual.)
The maximum number of Aether Crystals that a mage can consume during a ritual is equal to their Aether Channeling attribute. The value of this attribute is determined by a number of factors, such as whether they’re a Mystic or Arcanist, how many levels of the Mana Well ability they have, whether they’ve drunk a Brightblood Elixir or similar, and so on.