He says that part of the reason the Marie Antoinette pearl is worth so much is because it's a natural pearl, which brings us to one quality that determines a pearl's value. Natural versus cultured.

A great irony of pearl history is that the least expensive cultured pearl product in the market today rivals the quality of the most expensive natural pearls ever found. The price-value anomaly is ...

Natural pearls are harder to find ... There's a huge demand for black opal, with lack of supply driving up the price. Black opal costs from $1,000 a carat to tens of thousands of dollars.