Also like Braujou's weapon, it can withstand millions of tons of force. It may even be stronger than the spear.
No description for it's powers are given, but seeing how the Sacred Ancestor left it behind for a purpose, and how weapon is somehow presently hindering the Elder God's movements (having been used against him in their battle), it is not far fetched that it has powers of it's own. Affecting the elder it would have to have metaphysical along with physical damaging properties. At the very least it probably contains the Sacred Ancestor's will.