The Basic Dinosaur Egg Guide Many people often mistake a concretion for an egg, to help clarify what is a concretion, and what is a real egg, here is a guide.   A quick overview with examples:       How to spot a concretion:     How are they different from eggs?     A concretion is a rather common rock made of tightly compressed minerals. Typically, concretions are a smooth sphere or oval with little to no surface texture or