London: The “Hope Spinel,” once owned by famed gem collector Henry Philip Hope and part of the same collection as the famed Hope Diamond, is being offered for sale for the first time since 1917.

Set in a 19th century silver and gold brooch, the 50.13 carats octagonal-cut stone is the size of a small plum. Auction house Bonhams is expecting bids in the region of £150,000 to £200,000 ($227,542-$303,390).

“An incredible 98 years since it was last auctioned, the Hope Spinel is now for sale again for the first time since the original sale,” said Emily Barber of Bonhams. “It not only had the amazing provenance but it’s also an exceptional gemstone in its own right… You just don’t see pieces of this quality and provenance on the open market very often. It’s very exciting.”

Spinels are sometimes confused with ruby because they are found in the same rock formations, are chemically similar and often have a beautiful pinkish-red coloring. However, very large specimens are often more transparent and freer from inclusions than ruby.

The Hope Spinel will be auctioned on September 24 as part of Bonhams’ London Fine Jewellery sale.