I beleive it was the hope diamond but I'm not positive.

According to several sources that I found at ask.com, the largest diamond ever found was the 3,106-carat Cullian diamond which was found in 1905 in South Africa. On the other hand, according to http://www.si.edu/resource/faq/nmnh/hope.htm, the Hope Diamond was only 112 3/16 carats when it was first found. I don't know if there was a larger

The largest diamond to have ever been found (on this planet) is the "Cullinan I" . It bears its name after Sir Thomas Cullinan , owner of the mining company that discovered the diamond.Having been found in Africa,it is also very often aptly called the "Star of Africa" . This marvellous beauty weighs in at a whopping 530.20 Carats and boasts 74 perfect facets.Its was shaped by none other than Asscher in Amsterdam.It was cut out of a 3100 carat stone. It was set in the sceptre of King Edward VII , which resides in the Tower of London. Contrary to popular belief , the Hope diamond is simply "one" of the largest diamonds to have been found, and is in fact NOT the largest . Second in line after the Star of Africa is "The Excelsior".It originally weighed 995.2 carats. It was cut into 10 pieces, the three largest weighing 158, 147 and 130 carats. These pieces were then cut into 21 gems ranging from 70 carats to less than 1 carat. Not limiting this search to The Milky Way , A team of astronomers lead by Travis Metcalfe, claimed to have found a "Cosmic Gem" , a diamond in outer space weighing in at an astronomical 10 BILLION TRILLION carats !! ( 1 followed by 34 zeros ) It is the heart of a burnt out star ( carbon inside the dead star had crystallized when the star burnt out and eventually formed the diamond ). It is located in the constellation Centaurus , a distance of 50 light years away ! The distance of 50 light years can be equated with travelling 6 TRILLION miles each year for the next 50 years. It was christened "BMP 37093" For those not too familiar with 'diamond metrics' , 142 Carats equals 1 Ounce.

Cullinan I - also known as The Star of Africa was named after Sir Thomas Cullinan, owner of the mining company, and currently claims the title of largest cut diamond in the world. Of all the worlds largest diamonds Cullinan I is the largest. It was cut by Asscher in Amsterdam, weighs 530.20 carats, and has 74 facets. The Cullinan now resides in the Tower of London and is set in the sceptre of King Edward VII.

No one said anything about where the largest diamond was found. This one might prove to be a bit difficult to mine, but it would sure be interesting to see. Its named BPM 37093. Its the heart of a burned-out star and is a diamond that weighs in at a staggering 10 billion trillion carats.It would be hard to put a value on a diamond that large. But, just think of a mine with 2500 miles of diamond craters. “You would need a jeweller’s loupe [magnifying glass] the size of the sun to grade this diamond,” said astronomer Travis Metcalfe, who led the team of American researchers who found the cosmic gem. For over 40 years scientists have suspected that the interior of a white dwarf, the hot core left in space after a star burns all its fuel and dies, is crystallised. “The hunt for the crystal core of this white dwarf has been going on for decades but obtaining direct evidence only became possible recently,” said Michael Montgomery, the co-author of the paper announcing the discovery. The carbon core of BMP 37093, the scientists figured, had solidified into a giant diamond. Can you imagine wearing that on your finger? And, of course, aqnother problem would be how to get it. Its only 50 lightyears away in the constellation Centaurus, it would take you riding six trillion miles a year for 50 years just to get there. And, sadly, this giant diamond doesn't even sparkle at night. It is not even visible to the human eye. But this burned-out husk completely outshines the largest diamond on Earth, the 530-carat Star of Africa, the centerpiece of the British crown jewels. The Star of Africa was cut from the largest diamond ever found on Earth, a 3100-carat stone. BLING! BLING!