The Tables of the Law as they are widely known in English, or Tablets of Stone, Stone Tablets, or Tablets of Testimony (in Hebrew: לוחות הברית Luchot HaBrit - "the tablets [of] the covenant") in the Hebrew Bible, were the two pieces of stone inscribed with the Ten Commandments when Moses ascended Mount Sinai as written in the Book of Exodus. Exodus 31:18 refers to the tablets as the "Tablets of (the) Testimony".
According to the Bible, there were two sets. The first, inscribed by God, were smashed by Moses when he was enraged by the sight of the Children of Israel worshipping a Golden Calf; and the second, later cut by Moses and rewritten by God.
According to traditional teachings of Judaism in the Talmud, they were made of blue sapphire stone as a symbolic reminder of the sky, the heavens, and ultimately of God's throne. Many Torah scholars, however, have opined that the Biblical "sapir" was, in fact, the lapis lazuli (see Exodus 24:10, lapis lazuli is a possible alternate rendering of "sapphire" the stone pavement under God's feet when the intention to craft the tablets of the covenant is disclosed (24:12)).
According to the bible, both the first shattered set and the second unbroken set were stored in the Ark of the Covenant (the Aron Habrit in Hebrew).
In recent centuries the tablets have been popularly described and depicted as round-topped rectangles but this has little basis in religious tradition. According to Rabbinic tradition, they were rectangles, with sharp corners, and indeed they are so depicted in the 3rd century paintings at the Dura-Europos Synagogue and in Christian art throughout the 1st millennium, drawing on Jewish traditions of iconography.