exodus 24:10 And they saw the God of Israel: and there was under his feet as it were a paved work of a sapphire stone, and as it were the body of heaven in his clearness. - Free Bible Online

      10. And they saw the God of Israel--That there was no visible form or representation of the divine nature, we have expressly intimated (De 4:15). But a symbol or emblem of His glory was distinctly, and at a distance, displayed before those chosen witnesses. Many think, however, that in this private scene was discovered, amid the luminous blaze, the faint adumbrated form of the humanity of Christ (Eze 1:26; compare Ga 3:24).
      sapphire--one of the most valuable and lustrous of the precious gems--of a sky-blue or light azure color and frequently chosen to describe the throne of God (see Eze 1:26; 10:1).

JFB.