A model holds a pear-shaped perfect D color, Type IIA Flawless clarity diamond weighing 101.73 carats that will be offered for sale for the very first time on May 15, 2013 by Christie's auction house in Geneva. - 

There's a rare diamond set to be sold off at Christie's Auction House in Switzerland today, one that would surely put Kim Kardashian's over-the-top engagement ring to shame. It is the largest clear, flawless diamond ever to be offered at auction.

This diamond doesn't yet have a name. "We call it right now the 'absolute perfection diamond'," says Daniel Struyf, jewelry specialist at Christie's. He says this diamond is completely clear. It was pulled out of a diamond mine in Botswana. And it was cut from a 236-carat piece of ruff.

"This 101 carat is actually very big," he says. "It looks a bit like a little egg."

Struyf says that little egg is expected to fetch $20 million to $30 million. The diamond is classified as "flawless".

"That means there are no impurities in the diamond, but also from the outside there are no impurities," he says.

For example, nitrogen is an internal impurity. It can turn a diamond yellow. And on the outside? Not even a hint of a smudge. People have to wear gloves when they handle it.

"It is actually a group of diamonds that are chemically pure, and which represent 2 percent of all diamonds," Struyf says.

Polishing it took 21 months. "A lot of time I think is probably spent looking at it and figuring out what shape is going to maximize the yield from this piece of rock," says Michelle Graff, diamond editor at National Jeweler Magazine. "You know, what can we get out of this that will give us the biggest, best quality stone possible?"

Even Graff wonders who would buy this. Her best guess: an investor or a collector. Or a movie star.

"Look at somebody like Elizabeth Taylor," Graff says. "I mean she had huge diamonds and she wore them."

And Graff says based on past auctions, that $20 to $30 million price tag might be a lowball figure.