This is the knife which belonged to Torak (and, previously, Torak's Father), and first makes an appearance in Wolf Brother. It is described in more detail in Spirit Walker. It was described as a "leaf shaped blade of blue slate, and an antler haft bound with elk sinew." The blade is banded blue slate, and is shaped like a willow leaf. Torak's Fa had told him that the blade was of Seal Clan making, as his Fa's mother was a Seal. Torak's grandmother had given the blade to Torak's father when he reached manhood, then he had fitted the hilt himself. As his father lay dying, Torak's father had given Torak the knife.
Later in the series, we find out that a piece of the Fire Opal is concealed in the haft of the knife.