(necklace designed and created by Ernesto Moreira and to be seen at the Houston Museum of Natural Science)
though they can be yellow or green:
photo by Arpingstone
Garnets are classed as semi-precious (which doesn't imply they're less beautiful than precious jewels, it just means there's enough of them about to be useful. Garnet paper, for instance, has powdered garnet stuck onto it and is used as sandpaper, and garnets are also used to cut steel and to filter water).
There is another sort of garnet, which is a device for lifting cargo off ships, but that's a quite different word.
Possibly the most interesting thing about this word, though, is its derivation.
Word To Use Today: garnet. The loading-cargo word probably comes from the Dutch garnaat. The jewel word comes from the Old French grenat, red, from pome grenat, which means pomegranate, which comes from the Latin pōmum, apple, and grānātus, full of seeds.