Because productivity is too much effort. In my defence, it was paper writing-related curiosity that led me to Wikipedia, where I found this electron microscope image of a broken piece of mother of pearl/nacre by Fabian Heinemann. (In case you wondered, I wanted to check roughly how big nacre tablets were. And no, Wikipedia is not my only source for this ;)) So: this is what mother of pearl looks like when you zoom in a few thousand times.
Nacre is made of little tablets of aragonite stacked on top of one another and separated by sheets of organic matter. The way the tablets scatter light is what gives pearls their pretty, pretty shine.
(I have a thing for electron micrographs of biominerals. Actually, I’m a big fan of close-up images of pretty much anything. It’s like looking into the secret heart of things.)