Understanding "Internal Crystalline Structure"

An “internal crystalline structure” is part of the definition for minerals. To understand that definition, you need to understand what “internal crystalline structure” means. This is not as easy as the other parts of the definition because it is often something that you can't see. If you are lucky, the specimen will have crystals you can see, but even when a mineral specimen does not form crystals, its molecules are arranged in a specific pattern. That pattern of molecules is what the definition is talking about.


All of these specimens are made of the mineral quartz, but only the center one is recognizable as a crystal.
All of them have an internal crystalline structure.

Without specialized equipment, you can't look at a specimen and tell if it has that internal pattern. Instead, you need to identify the specimen first. Once you know what it is, then you can use reference books or websites to determine if it has an internal crystalline structure.