Above over the heads of the beasts there was a firmament, which was fashioned as it had been of the most pure Crystal, and that was spread out above upon their heads:

And as I looked, behold, in the firmament that was above the cherubims there appeared the similitude of a stool of sapphire upon them.

Above the firmament that was over their heads, there was the fashion of a seat, as it had been made of Sapphire. Upon the seat there sat one like a man.

And before the seat there was a sea of glass, like unto crystal, and in the midst of the seat, and round about the seat, were four beats full of eyes before and behind.

and saw the God of Israel, and under his feet as it were a brick work of sapphire, and as it were the fashion of heaven when it is clear,

Gold is brought out of the North, but the praise and honour of God's fear cometh from God himself.

And he that sat was, to look upon, like unto a jasper stone, and a sardine stone: And there was a rainbow about the seat, in sight like unto an emerald.

having the brightness of God. And her shining was like unto a stone most precious, even a Jasper clear as Crystal:

Treasury of Scripture Knowledge

Summary

And the likeness of the firmament upon the heads of the living creature was as the colour of the terrible crystal, stretched forth over their heads above.

Bible References

The likeness

Above the firmament that was over their heads, there was the fashion of a seat, as it had been made of Sapphire. Upon the seat there sat one like a man.
And as I looked, behold, in the firmament that was above the cherubims there appeared the similitude of a stool of sapphire upon them.
and saw the God of Israel, and under his feet as it were a brick work of sapphire, and as it were the fashion of heaven when it is clear,
Gold is brought out of the North, but the praise and honour of God's fear cometh from God himself.
And he that sat was, to look upon, like unto a jasper stone, and a sardine stone: And there was a rainbow about the seat, in sight like unto an emerald.
having the brightness of God. And her shining was like unto a stone most precious, even a Jasper clear as Crystal:
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