What is the prime characteristic that geologists use to separate minerals into classes?

A mineral is a naturally occurring,inorganic, crystalline substance that aggregate to form rocks. Geologists separate minerals into classes based on their chemical composition. The different classes of minerals include halides, oxides, phosphates and sillicates.  Rocks are usually classified based on the grouping and composition of minerals in rocks. 

Where is the map from the question?

This could be considered an example of astrology.