What is the annual retail diamond market?  The US market?
What percent of that is engagement rings?

I asked a CEO of a diamond company what he thought.  Here is what he said. 


Worldwide diamond jewelry is about 100 billion.
The US is about 50% of that number.
World wide engagement I can't say but in the US there are 2 million
marriages a year.
Say the average ring is about 3000 dollars (wal-mart etc) so figure 6
billion on engagement rings.
I know this stuff from our pitch to investors and business plan.