The single most useful thing to know about lapis lazuli is that for most of recorded antiquity it was called sapphire.
The Hebrew sappir of the Bible, the Greek sappheiros, and the Latin sapphirus denote lapis lazuli, not the blue corundum that the word means today. The evidence is direct rather than inferential. Pliny the Elder describes sapphirus in the Natural History as a blue stone flecked with gold, which is lapis with its pyrite inclusions, and is not a description of corundum, which has no such flecking. Blue corundum was in any case scarcely known in the Mediterranean before the Roman imperial period. Theophrastus, writing in the fourth century BC in On Stones, describes the same gold-speckled blue material.
The consequences are wide. The sappir of the priestly breastplate in Exodus is lapis lazuli. The pavement of sapphire stone beneath the God of Israel in Exodus 24 is lapis. The throne of sapphire in Ezekiel 1 is lapis. Every medieval and early modern lapidary that discusses the virtues of sapphire before roughly the thirteenth century is discussing, or is drawing on sources that were discussing, this stone.
This is a checkable historical point and not a matter of interpretation, and it is one of the most consistently mishandled facts in popular gem literature, where the biblical passages are routinely illustrated with blue corundum. Where an old text says sapphire, the burden is on the reader to establish which stone is meant, and before the high medieval period the answer is usually lapis.