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Question 1 of 10
Halley's Comet black opal: the largest uncut black opal in the world.
This fist-sized opal was unearthed in 1986 at Lightning Ridge, Australia. Its most recent asking price was $1.2 million.
Question 2 of 10
The Allnatt diamond: a rare 101-carat "Fancy Vivid Yellow" diamond.
The Allnatt's most recent sale price, in 1996, was $3,043,496.
Question 3 of 10
The Chloe diamond: largest round brilliant-cut diamond ever auctioned.
The founder of Guess Jeans bought the diamond for $16.2 million in 2007 and named it after his daughter.
Question 4 of 10
The Wittelsbach diamond: the most expensive diamond ever bought at auction.
A London diamond dealer bought this 35-carat blue diamond for $24.3 million in December 2008.
Question 5 of 10
The Hope diamond: legendary 45.52-carat blue diamond.
no one knows
The "cursed" Hope Diamond isn't for sale -- it's on display at the Smithsonian -- and estimates of its value vary wildly.
Question 6 of 10
The Lesotho Promise diamond: golf-ball-size diamond found in 2006.
A South African diamond company bought the Lesotho Promise for $12.4 million and cut it into 26 diamonds. The hope was to make $20 million from the sale of the cut diamonds.
Question 7 of 10
The Big Pink pearl: the second-largest natural abalone pearl ever found.
The Big Pink pearl was appraised at $4.1 million in 1991, a year after it was discovered.
Question 8 of 10
The Pearl of Allah: the world's largest pearl.
The Pearl of Allah, otherwise known as the Pearl of Lao-Tzu, isn't iridescent like most pearls -- basically, it looks like a 14-pound lump of porcelain. But it's extremely valuable (and, like most famous gemstones, shrouded in mystery). The San Francisco Gem Laboratory valued it at $42 million in the 1990s.
Question 9 of 10
The Moussaieff Blue diamond: the most expensive per carat gemstone ever bought at auction.
In 2007, London jeweler Moussaieff paid $1.32 million per carat for this 6.04-carat flawless ring-set blue diamond -- a total of almost $8 million.
Question 10 of 10
The Amsterdam diamond: the most expensive black diamond ever bought at auction.
This 33.74-carat pear-shaped black beauty sold for $352,000 in 2001.