Exodus 24:10, 16

and they saw [a manifestation of] the God of Israel; and under His feet there appeared to be a pavement of sapphire, just as clear as the sky itself. [Ex 33:20-23; Deut 4:12; Ezek 28:14]

The glory and brilliance of the LORD rested on Mount Sinai, and the cloud covered it for six days. On the seventh day God called to Moses from the midst of the cloud.