Tephra are fragmental materials mined from rock formations within Zalcano's prison beneath Prifddinas, granting 35 Mining experience per tephra mined. Rock formations that are glowing will yield tephra at a much faster rate. The Varrock armour's double ore mining effect works here as well.
These are refined in the furnace to the east to create refined tephra, then imbued at the altar to create imbued tephra, which is used to deal damage to Zalcano's stone armour.
There is a 1/127 chance that a crystal shard will be obtained while mining tephra.