Shard

A Shard of Adonalsium, or Shard for short, is an aspect of the power of Adonalsium in the cosmere. Adonalsium was at one point a single, unified power with unknown abilities (though based on what the Shards can do, they are assumed to be quite spectacular). However, in a manner that we do not yet understand, Adonalsium was shattered, and various people became somehow bonded to the various pieces of the whole.

Known shards

It is widely believed that there are sixteen Shards. Though this has not been confirmed, there are several passages in cosmere books that hint at there being sixteen Shards. Each Shard is associated with an emotion or idea, and over time, the personality of the Shardholder changes to more closely match the concept that their Shard embodies. For example, in The Way of Kings, we are told that Ati, the holder of Ruin, was once a kind and gentle man. However, when we see him in the Mistborn Trilogy, he is known only as Ruin, the essence of destruction, and is currently attempting to destroy the world.

Other known Shards include Preservation, Endowment, The Almighty, Cultivation, and Odium. Known Shardholders include Rayse, Bavadin, Sazed, Aona, and Skai. Hoid also is confirmed to have knowledge of Adonalsium. Though it seems unlikely that he is a Shardholder, and his motivations and plans are not yet clear, Hoid was present at the Shattering of Adonalsium, and it seems that his hidden agenda is likely related to the Shards in some way.

As of The Way of Kings, it has been confirmed that a Shard of Adonalsium can be further shattered, a process known as Splintering. The only known instance of this occurred with the Shards held by Aona and Skai after Rayse killed them during his visit to Sel.

Abilities

It is not entirely clear what abilities each of the Shards have. They seem to be limited in some ways by the idea their Shard embodies - for example, neither Ruin nor Preservation was able to create on their own (as creation was contrary to the nature of their Shards), but when they worked together, they were able to create life on Scadrial. Endowment is apparently able to bring certain individuals back from the dead on Nalthis. The capabilities of the Shards on Sel are unknown, as both Skai and Aona were dead by the time the events of Elantris took place. The only known Shards on Roshar are The Almighty and Cultivation. The Almighty is confirmed to be dead, and we have as of yet seen nothing of Cultivation, meaning we know very little of their influence on Roshar. It seems likely that the Ten Heralds and the Knights Radiant are related to the Shards of Adonalsium as well, though it is not yet entirely clear how.

Relationship to magic systems

It also seems that the Shards are directly related to the magic systems on each world, though how and to what extent seems to vary from Shard to Shard and world to world. In Mistborn, Allomancy stems directly from Preservation, and Hemalurgy directly from Ruin. Feruchemy seems to be caused by the interaction of the two. Awakening from Warbreaker is also likely a result of the Shards there. Aon Dor is a little trickier to explain, as we know that the Shards present on Sel had been Splintered by the time Elantris takes place. Also unexplained are the strange magics used by the Dakhor monks. At this time, Shards remain the only known source of magic in the cosmere, though it has been speculated that the Old Magic in The Way of Kings could stem from a different source.