A cryptocurrency entrepreneur who paid more than $4 million for the world’s largest black diamond allegedly purchased the rock with proceeds from a $1 billion crypto fraud. The SEC on Monday announced fraud charges against Hex founder Richard Heart, also known as Richard Schueler. Heart marketed the ethereum-based Hex token as the first blockchain certificate of deposit and promised to reward users who agreed not to trade or sell their tokens for a preset time. “The longer lockdown period you choose, the higher interest rate you receive,” according to an ad. Heart flaunted luxury items to draw…