The honor of “Most Rare and Expensive Gem” goes to the Pink Star Diamond. This stunning beauty weighs in at a hefty 59.6 carats. When it was put up on Sotheby’s auction block in 2013, the Pink Star went for a jaw-dropping $83.2 million. However the auction winner defaulted on the payment and this vivid pink diamond now sits in Sotheby’s inventory, valued at $72 million. This valuation puts the Pink Star in at $1,208,053.69 per carat.