AugustinaJewelry Single Strand 18 Inch 6-7mm Black Freshwater Cultured Pearl Necklace

After purchasing this necklace, I learned a few things about natural pearls:
No two are identical. They are formed inside an oyster as a defense mechanism against an irritant that becomes lodged in the creatures tissues. The oyster does care if it is not perfectly round.
There is no such thing as a naturally black pearl. They are dyed to resemble a blackish color. Each pearl has different porosity an thus absorbes different amounts of dye. Therefore the color is not uniform from one pearl to the next.
When the jeweler measures each pearl, he/she measures it at the widest point. So, a 7mm pearl may be only 5 mm at it's narrowest diameter.
So the necklace I received was not what I was expecting, but the merchant does offer a 100% satisfaction guarantee, so I was invited to return it if I was not satisfied.