Ezekiel 1:22

(Verse 22 onwards) And the likeness above the heads of the living creatures was like the appearance of a crystal dreadful ice; extended above their heads was what appeared to be a firmament. Under the firmament their wings were straight, one toward another. Each of them had two wings that covered their bodies, and each one had two wings that covered one side. And I heard the sound of the wings, like the sound of many waters, like the sound of the Almighty God.

"And the likeness over the heads of the living creatures was of a firmament, like the appearance of terrible crystal, stretched above their heads." With the Lord's generosity, we shall explain these things in two ways, so that we may leave it to the reader's judgment to decide what should be chosen. For by the name of firmament, the heavenly powers can be understood. This firmament is rightly said to be like the appearance of crystal, because crystal is indeed exceedingly strong, yet it is solidified from water. And the angelic nature, when it was created, received free will—whether it wished to persist in humility and remain in the sight of almighty God, or whether it would slip into pride and fall from blessedness—it was like water by comparison. But because, while others were falling, the holy angels persisted in their blessedness, and received this as a gift, that they could no longer fall at all, their nature in them, because it can no longer be led about changeably, was hardened as if into the solidity of crystal. This crystal is said to be terrible and stretched out over the heads of the living creatures, because those angelic powers which stand in the presence of almighty God are terrifying and fearful to us who are still placed in this corruption. Their joys, because they exceed the perception of our minds, are said to be above the heads of the living creatures. For who, placed in corruptible flesh, could comprehend what that ineffable and endless joy of the angels might be? What blessedness it is, to see the face of the Creator without failing, and to persist in delight in Him without change? However, by the name of firmament, our Redeemer himself can be understood figuratively—true God above all things, and made perfect man among all things, in whom our nature has been confirmed with the Father. […]

Likeness - The appearance or resemblance. As crystal - For splendour, purity, and solidity, all that was above these creatures and wheels was beautiful and very majestic, and 'tis therefore called terrible, because it impressed a veneration upon the mind of the beholders.

The color of the terrible crystal - Like a crystal, well cut and well polished, with various faces, by which rays of light were refracted, assuming either a variety of prismatic colors, or an insufferably brilliant splendor. This seems to be the meaning of the terrible crystal. Newcome translates, fearful ice. The common translation is preferable.

“The color” (Hebrew, “eye”) “of the terrible crystal” refers to the dazzling brightness of the “firmament,” a clear bright expanse between the “throne” and the “living creatures,” separating heaven from earth.