What was the First album to sell one million copies?

There are actually two that are listed as the first to sell one million copies, and it is debated which reached the feat first. They are "Calypso" by Harry Belafonte and "Elvis Presley" by Elvis Presley.

Both were released in 1956, and both made it to No. 1 on the charts. However, Calypso spent an incredible 31 weeks at the top, which would seem to support that it reached the one million milestone first.