What is the highest selling gem?

I'm curious, what is the most sought-after and highest selling gem in the market today? Is it a rare diamond with exceptional clarity and color, or perhaps a vividly hued sapphire that captivates the eye? Is there a particular cut or origin that drives up the price of a gem, making it the most popular among collectors and investors? I'm eager to learn more about the characteristics and factors that contribute to a gem's status as the highest selling in the world.