When I launder my clients shirts in Winter, I dry them in the dryer at the 'no heat' setting unless it is a sunny day - in which case they are hung. I have NEVER seen a button chipped in this manner. HOOOOOWEVER ... I have
seen about a gazillion and a half cheap sh.. "pearl" buttons. These are cut from the outermost rim of the shell where the layers (one per year, just like the rings on a tree) are the newest and the thinnest. If you view them from the side, you can actually see the layers. Until these have aged and become a more solid, unified mass, you can break the layers apart with your fingernail or a nail file, just as you would disassemble a piece of mica. An oyster shell is made up of many layers. There is the outer shell which looks like a mottled, crusty mass. The inside of the shell looks like an irridescent pearl. At a very specific point, this inner pearl shell ends and the outer shell begins. The colors you see on the back of cheap (sorry.) pearl buttons indicate that the back is constituted of the outer layer. You don't need Carl's hammer to break off (chip) the outer layer. A feather will do that just as easily. That is why real, good, pearl buttons cost almost a buck each.
On the left is shown the inside (pearl side) of the oyster. This one is about 60 years old and measures 9" across. Along the bottom, you can see some of the layers. The center picture shows the back of the shell where you can see the outer layer. You can also see where I have chipped off parts of the outer layer to demonstrate the above thesis to clients over the years. On the right is a side shot. Here you can see that the shell, at its thickest point, is about 1" thick. The thinnest part, around the perimeter, is also the most plentiful. Hence, it offers the cheapest substance that can be called M-O-P. The farther toward the center you travel, the thicker the button. At the 4mm thick point, you are about 2" in. You can see how many fewer really fine shirt buttons can be taken from this much smaller diameter. Now, as to Carl's If I Had A Hammer
demonstration ... you can shoot 45 cal. bullets at Lexan acrylic and they won't go through. However, heat it with a simple match ... and it will simply melt. Lexan wasn't designed to stop heat, and pearl buttons weren't meant to protect you from a hammer wielding serial killer. On the other hand, I have dyed some of my M-O-P buttons by glazing them and heating the to 1975 degrees in my clay kiln. In fact, though, Carl is correct. Pearl is nowhere near as shatterproof as some of the modern plastics. That doesn't mean it should chip in a dryer. Take the shirts back or invest in a few of your own buttons.