Sales for pink diamonds have been rising and rising over the past few years. The larger rare stones aren't just beautiful to look at, they are considered money in the bank for investors. The market gets another test next month when Christie's brings a 10.09 Fancy Vivid purplish-pink diamond up for sale as part of its Magnificent Jewels sale in New York April 12. JCK Online reports that the diamond is estimated at $12 million to $15 million. The record for pink diamonds belongs to a 24.78 carat stone which sold for $46 million at Sotheby's last year.