They study the:

* Composition: What elements and compounds make up a mineral.

* Structure: How the atoms are arranged in the mineral's crystal lattice.

* Properties: Physical and chemical characteristics like hardness, color, luster, and cleavage.

* Formation: How minerals form in geological processes.

* Occurrence: Where minerals are found and how they are distributed.

Mineralogists work in various fields like:

* Geology: Studying the Earth's composition and history.

* Mining: Finding and extracting mineral resources.

* Material science: Developing new materials with desired properties.

* Gemology: Identifying and evaluating gemstones.

There are also specialized fields like petrologists who study rocks and geochemists who study the chemical composition of the Earth.