Jade tablet, tapering in thickness towards the size, suggesting it might be a huge, ceremonial blade. Qijia culture (2300-1600 BC). Engraved writing added much later, IIRC there was a sign about someone (IIRC an Emperor) having some of his writings engraved on a number of old jade pieces, but it seems I forgot to photograph that. Note that the museum does not bother to orient the tablet so the writing is right-side-up.