Black diamonds are pretty much diamonds that are still in the carbon stage so they didn’t have enough time, pressure or heat to become crystalized like the rest of the diamonds are.

Black diamonds’ value is often one tenth of a regular diamonds but it will depend on the size and shape. Obviously if it is a really large black diamonds price could go up to thousands but will still cost fraction of a regular diamond in the same size. Also there isn’t any brilliance because they don’t let the light to reflect back from the facets. They tend to look dull black like onyx.

Without seeing the diamond ring listed on Amazon.com it is hard to estimate it’s value but you should ask the weight and quality of diamonds at both places to make a decision.

Once final thing black diamonds might be the trend right now but once it passes their value even drops lower so they won’t retain their value for the future.

Personally I would go with the Amazon.com and if you really hate it you can always return it for a full refund. I don’t think I can say the same thing when you buy it from a local shop.

Good luck!