The heaviest diamond found to date was found in 1906 in South Africa, and it weighed more than 3,100 carats. Physically, it filled the palm of a grown man's hand.
'Most expensive' indicates that records of sale exist. There are diamonds that have always changed hands otherwise, for example, as spoils of war (Kor-i-Noor, currently in the British Crown Jewels),...
Any diamond cut is 'difficult' given the inherent high value of the raw material that the diamond cutter works with. Every diamond cut is planned. Planning the cut aims to maximize the raw stone's...