Nacreous = Mother of Pearl

Nacre also known as mother of pearl, is an organic-inorganic composite material produced by some molluscs as an inner shell layer; It is strong, resilient, and iridescent.
(Wikipedia)

The main commercial sources of mother of pearl are the pearl oyster, freshwater pearl mussels, and to a lesser extent the Abalone, Widely used for pearl buttons especially during the 1900s.
(Wikipedia)

Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light. These structures interfere constructively and destructively with different wavelengths of light at different viewing angles, creating structural colours.
(Wikipedia)

Amongst a couple of other shells here there are are two Abalone shells, the larger one was given to us fresh from an abalone fisherman, just the other week.
The first Sunday in every month the fisheries dept. allow Abalone fishing from the rocks in the ocean here at Mindarie, we were walking Milo at the time and the fisherman was handing one to each person who passed, we suspected he had fished more than he was allowed as the fisheries inspectors were just further ahead, it's closely monitored and regulated that only a certain weight/size is allowed to be fished.
Glyn cleaned it, and so the poor Abalone didn't die for nothing I kept the shell, now it's stored in my glass jar that's full of other shells that's been collected over the years.