Diamonds are a girl's best friend - providing she, or the person who bought one for her doesn't mind paying for one on a credit card, with interest, for the next ten years of their life. There aren't many practical uses for a diamond other than decoration, and as millennials tend to have lower disposable incomes than their parents, they don't have the budget to spend big on shiny bits of rock.
The decline of marriage among young people has had a knock-on effect on diamonds. Fewer under-35s than ever before are getting married, and those who do are increasingly using cheaper alternatives than diamonds when buying rings. In response, companies who sell diamond rings are currently working out how to change their marketing to bring millennials back on board. We imagine that a sharp drop in prices might help a little.