Greenstone polyhedron inscribed with letters of the Greek alphabet 2nd–1st century B.C.
The polyhedron has 20 sides, each inscribed with a letter of the Greek alphabet from A (alpha) to Y (upsilon), so that only the last four letters (phi, chi, psi, and omega) are missing. See a faience example (37.11.3) also displayed in this case.
Source: metmuseum