Rick mentioned studies that he read, but didn't give me any links, so you'll just have to do your own googling on that one.
As for the video blogger I mentioned, "Girl Writes What":
YouTube Channel
The video with her comments I was specifically referencing during the episode - "Women on pedestals can only fall" with Stefan Molyneux
Links provided by Andy:
DeBeers (wikipedia)
Age of Persuasion also had a bit on the marketing of diamonds