Great Kanohi, or Great Masks, were Kanohi Masks of Power with an enormous amount of power.2 They could be used effectively only by Toa.1 They were made from Kanoka disks of power level 8.2, 1, 3
Toa's Great Masks were physically tougher than Matoran masks. They were not as easy to break, and as stated in BIONICLE: Mask of Light (Novelization), they did not melt in lava. However, they should not have been left in lava too long. The flames of the Ta-Metru furnaces burned hotter than molten protodermis, which is why masks could be melted for casting and not automatically in lava.4