When I was young, a shop proprietor once told me how to differentiate real pearls from the fake. You take a a cutter (or scissors) and scrape across the surface of the pearl, you should get a creamy residue or pearl cream that you can rub into your skin like moisturizer.
I wouldn't recommend it for your legacy/heirloom pearls or anything that costs upward of $10K. But, it is an excellent guide for all others; seed, freshwater or cultured pearls. I have a preference for the real stuff because of this very reason. I own neither plastic pearls nor their more expensive cousin shell pearls (layers of pearl powder painted onto a seed pearl).
I am lucky to be in a city where hobbyists have easy access to wholesale strands of the real stuff for lapidary purposes. So when I do buy something from the jewellery shop, it has to be special. My favourite piece is the pendant above. A white gold and diamond 3D hoop (although the picture looks kinda flat) with a glossy black Tahitian pearl nestled in the middle. The setting is quite amazing and I am happy to report, it hasn't dropped off yet.
Not to be confused with the naturally formed & expensive odd shape Baroque Pearls. Mabe pearls are a cheap and strangely wonderful form to have in any collection. Like an egg contained within a metal ring in a frying pan, Mabe pearls are only occasionally found in nature. They are usually formed by planting a hemisphere shape seed or removing a seed pearl from the tissue and transplanting it into the shell to grow. My favourite piece is this greyish colour set in palladium.
Hailing from the oceans of Australia, Indonesia and Philippines. Golden South Sea pearls are both rare and exotic. The rich lustre beckons a second look. I only own 2 pieces; a necklace and a yellow gold diamond ring that is shaped like a bow. Kinda traditional, but when you realize how difficult and expensive golden pearls can get...traditional works fine for me.
My wish list: More Tahitian pearls, in every colour they can possibly come in. A strand of Akoya pearls in all their perfectly formed super shiny-ness. And maybe more odd shaped and unusual varieties. *sign* wish I made more money... =P