The crystal system a mineral belongs to relates most to the mineral's

Mineral's interior atomic structure

Explanation:

The interior atomic structure of a mineral refers to the system of arrangement and orientation of the atoms within the crystals. They are made up of fundamental unit cells and continue their arrangement periodically in a three-dimensional system.

There is a total of six crystallographic systems and they all have their own characteristics for identification. They are as follows-

1) Isometric system

2) Orthogonal system

3) Monoclinic system

4) Triclinic system

5) Orthorhombic system

6) Tetragonal system

The study of the arrangement of these atomic crystal plays an important role in the field of mineralogy and further, by observing these structures, a mineralogist can determine to which crystallographic system a mineral belongs.