Prismarine Crystals

Prismarine Crystals are items obtained by defeating guardians and elder guardians.

As a drop from Guardians
Prismarine crystals are dropped by Guardians or Elder Guardians. 0-1 are dropped each time.

The drop only happens if the raw fish drop fails. Looting I gives the best chance (27%).

From sea lanterns
Prismarine crystals are dropped by sea lanterns when not using a silk touch pickaxe. They drop 2-3 crystals each time, which can be increased to a maximum of 5 using the fortune enchantment.

History
Cristaux de prismarin pt-br:Cristais de Prismarinho 海晶砂粒