What is the most expensive GEM of all time?

I'm curious to know, what exactly is the most expensive GEM, or gemstone, to have ever been sold? Is it a rare diamond? Perhaps a stunning emerald or a breathtaking ruby? I'm eager to find out which of these precious stones holds the title of the most valuable GEM in the world, and what factors contributed to its exorbitant price tag. Is it the rarity of the stone, its exceptional quality, or perhaps a combination of both? I'm intrigued to learn more about this extraordinary GEM and its unique history.