Where do black pearls come from and how are they produced?

Question

I know that most pearls including black pearls are lab created and do not occur naturally.

Answer 1

Colour in pearls is a complex matter but very basically there are two areas to be looked at. The greatest number of black pearls you will see are not in fact black but other colours which have been stained black by man. 99% of these are cultured but a very few natural pearls with very unattractive colours are also stained. Natural black pearls come almost exclusively from the Pinctada margaritifera oyster. The colour is due to chromatophore in the albumen in the pearl strata. Also the mineral content, salinity and depth of the water can have a large effect on pearl colour.
The main production areas are the Touamotou and Gambiers Archipelagos and the Marquises Islands. Other areas but to a lesser extent are the Red Sea, Panama, Fiji and Mexico.

Answer 2

Different bivalves roduce different colors of nacre, (the substance secreted to line their shells and protect them from irritants).
When a sand grain gets into one that produces a black nacre, a black pearl may result.