The Graff Ruby is expected to make $6.8m-9m when it auctions at Sotheby's Geneva on November 12.
Described as "pigeon blood red", the 8.6-carat stone is mounted on a platinum and diamond ring. It was named for its previous owner, jewellery magnate Lawrence Graff, who bought it for $3.6m at Sotheby's in 2006 - setting a per-carat auction record.
A flawless 8.4-carat pink diamond valued at $12.8m-15.4m will auction at Sotheby's Hong Kong on October 7.
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