The Pink Star Diamond — $71.2 million (2017)

The Pink Star Diamond set the auction record for any gemstone at $71.2 million when sold at Sotheby's Hong Kong in 2017. This 59.60-carat internally flawless pink diamond, mined in South Africa in 1999, required two years of cutting and polishing to achieve its cushion-cut brilliance. It is one of the rarest Type IIa diamonds, making up less than 2% of all natural diamonds.