What are all these HPHT diamonds on EBay?

I am curious about the “diamonds”that are being sold on eBay for so dirt cheap. They are often a blue green.

We’re talking like cubic zirconium prices set in 925.

Yet, the sellers insist that they are real diamonds, just pressure treated, and they are long-term sellers with a good rating.

I am curious, I would like to buy one just to try, but I don’t want to buy something that’s really really fake for a couple hundred dollars

Thanks in advance, I see the HPHT diamonds discussed online, but they’re expensive. I just can’t decide if they’re fake and nobody’s paying much attention to what they buy.

CVD I suppose too. Same idea.

Hoop Dreams Inc is one example of a seller.