You’ve undoubtedly seen plenty of rubies, garnets, and other scarlet stones, but odds are, not a red diamond. Considered even more unusual than pink or blue diamonds, red diamonds are widely known as the rarest (and therefore, most expensive) diamonds in the world—in fact, for 30 years (1957–1987) the Gemological Institute of America graded none with the pure color. But now, Heritage Auctions is presenting the opportunity for one lucky person to own a diamond of the sort—and a 1.21 carat one, at that—in its upcoming Fall Fine Jewelry Signature Auction on Sept. 29.

“This gem is one of only a few diamonds to display enough saturation and intensity to be graded as a true red,” Jill Burgum, Heritage Auctions’ executive director of fine jewelry, said in a statement. “Adding to the allure, the cause of a red diamond’s color remains a mystery to scientists, making this stone even more of a marvel.”

Another highlight from the sale isn’t as rare, but coming in at 17.63 cts., it carries its own weight. Boasting a massive fancy intense yellow diamond surrounded by more than 2 carats of baguette-cut diamonds, the ring is from the estate of Dallas philanthropist and civic leader Mary Anne Sammons Cree. One of 125 pieces on offer from the estate, this ring is accompanied by jewels including Cree’s platinum and 18k gold necklace with approximately 25.75 cts. t.w. Asscher-cut yellow diamonds (estimated to go for $80,000–$100,000 and with a retail value of $340,000) and plenty of others. The proceeds from all of her jewelry will benefit Communities Foundation of Texas and Dallas-area nonprofits.

Top: The 1.21 ct. round brilliant-cut fancy orangey-red diamond, estimate:  $100,000–$150,000 (photos courtesy of Heritage Auctions)

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