The abalone pearls like those in your ring are natural. Cultured abalone pearls are a fairly recent development. As far as I know, the only abalone pearls being cultured are coming out of New Zealand, using the paua species, a smaller species with intense blues and greens. I had the pleasure of visiting the farm a few years back and saw the nuclei used - they reminded me of white plastic teddy bear eyes -low domes with a stem on the back to secure them within the shell. Thus, cultured abalone pearls are regular in shape, not freeform. I only saw round mabes, though I suppose other shapes would be possible - teardrops, hearts, etc.
