A GIA-certified 10 carat diamond costs between $167,200 to $2,245,100 at wholesale. The price can vary depending on the quality of the diamond. A 12 carat diamond costs between $230,600 and $3,196,000 at wholesale. A 15 carat diamond costs between $315,000 and $4,260,000 at wholesale. A 20 carat diamond costs between $500,000 and $6,540,000 at wholesale. A 30 carat diamond costs more than $1 million at retail. Yellow diamonds are diamonds that contain carbon in its elemental form (carbon). Diamonds are formed deep within stars when layers of gas and dust collapse under their own weight forming supernovae. These remain intact for a long time before exploding, leaving behind elements such as nitrogen, phosphorus, and sulfur along with large amounts of carbon.