So two main types of structures exist, and we'll talk about Crystalline Solids or simply crystals and amorphous solids. So let's begin with the crystalline solids. So all Crystalline Solids or simply crystals have a very well ordered shape or structure. And because of that, they have a very sharp melting point. What that means is that the melting point's range is very small. It melts over a very, very small range of temperature.