What is the difference between Pearl (pictured to the left) and and Mother of Pearl? (pictured on the right. )
Simply this - Mother of Pearl is the inside lining of the shell - virtually all shells have it. A pearl is the same lining material - deposited by the living creature over an irritant that has gotten inside the shell.
Right away - you can see that there is a LOT more Mother of Pearl available to be made into things than Pearls - even with the extensive pearl culturing that is done now.
Mother of Pearl tends to be limited to shapes that can be cut out of relatively thin material. Think of a clam or an oyster or a mussel shell from your last trip to a fancy seafood restaurant. If you were to cut that shell up into beads, you can see that you might get a large flat round from the middle, and some smaller rounds from around the sides. It's sort of a puzzle - like figuring out the most efficient way to lay out a pattern on a piece of fabric. The Mother of Pearl items can't be any thicker than the thickest part of the shell. Unless you started gluing layers together. That's why Mother of Pearl is very prominent in traditional inlay designs, like in furniture. It comes in small flat pieces anyway!
That darker, rough part of the outside of the shell is taken off - and it is shiny, pearl stuff right underneath, btw.
Pearls, however, are cultured by inserting an irritant - usually the mantle tissue (part of the body of the creature that lives inside the shell) of another shell or mantle plus a piece of mother of pearl! - into the oyster. Cultured pearls come mostly from oysters - with the centre part coming from a mussel shell. We've seen a trend towards putting funky shapes into oysters so that they will encase a cross or flower shape with pearly material.
A pearl is essentially an immune-system reaction. Or, like dealing with a particularly ugly piece of furniture. If I can't get rid of this annoying thing in my house, maybe I can paint over it.
We could also think of pearls as Oyster Snot - but I'm guessing that this doesn't have much marketing potential. ;-) Ooo - I see your boyfriend got you those Oyster Snot earrings you were looking at last week. Nahh - that's not going to fly with anyone.