It's just extra calcium. Sometimes it happens. We get so used to perfect eggs when we buy them in the store that we forget that not all eggs are the same. Egg farms grade all their eggs. Ones like yours wouldn't make it to the store. They also remove the double yokers, ones that are too large and ones that are too small. There are several things that can cause an egg to be like yours. The calcium spots can be caused by a shell gland that has a problem, some disturbance while the egg was forming, or feeding too much calcium. It's still a perfectly good egg to eat. Your bird doesn't have some disease.