My own hypothesis on the nature of Primals [SPOILERS]

[treuhavik]

The primals themselves may actually be smaller pieces of the Twelve, just like how the egi are also smaller pieces of the primals.

Exactly. Think of the Twelve as clusters, Primals - crystals and Egis, shards. But for each cluster there is an astral and umbral crystal. We've just yet to see these astral crystals or full clusters in use. :P