Today, emeralds may be a bit less famous than their red, white, and blue cousins—diamonds, rubies, and sapphires. But they were once perhaps the most celebrated gemstone.

3,500 years ago, the Egyptians found emerald deposits in their kingdom. They ascribed to the stones many mystical properties.

They were symbols of fertility and immortality, perhaps because of their “ever green” color. They were thought to increase eloquence and intuition. Some even thought they could cure malaria.

Those who put emeralds under their tongue could supposedly see into the future.

Perhaps for these reasons, Cleopatra was a big fan, as were other celebrities of her era, like Alexander the Great.

Stars of a more recent time, like Elizabeth Taylor, also loved emeralds, but probably more for their rare color.

And it is quite rare. Emeralds can only form when two scarce elements, beryllium and chromium, happen to occur in the same place in sufficient quantities.

The resulting crystal, more accurately called “green beryl,” is not quite as hard as diamonds, sapphires, or rubies.

Though rare, in the last few centuries we’ve found deposits in other countries, with Colombia producing the greenest stones.

The largest emeralds ever found—nine staggering crystals the diameter of your forearm—sit in a vault in the LA County Sheriff’s office.

These uncut stones, worth nearly 400 million dollars, are surrounded by intrigue, a story perhaps we’ll cover on another EarthDate.