The plot thickens a bit...
When starting this thread, I really didn't know that there is at least one species of Abalone that does have white nacre - the 'Mule Ears'! By their fancy name: Haliotis Asinina (Linnaeus).
'Guess now the question is: does anyone know of pearls from these shells at all?
As far as I understand, these things are cultured (link to one source of reports from
Thailand) for meat and shells too, but not for pearls.