A sapphire is a precious gemstone that is most often deep blue, though it can come in other colors. It is very hard and is used in jewelry and some special tools.
From Old French *safir*, from Latin *sapphirus*, from Greek *sáppheiros*, which probably referred originally to a blue stone like lapis lazuli. The term later settled on the blue variety of corundum.
Rubies and sapphires are actually the same mineral; if it’s red we call it ruby, and almost any other color becomes sapphire. The word that once meant any deep blue stone is now laser‑specific to a crystal structure. Our naming of gems is a mix of poetry, confusion, and later science.
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