## Math in the Natural Sciences## Math in Geology |

## How are the shapes of crystals classified? |

Geometry plays an important part in the study of minerals. This is because certain minerals exhibit specific shapes called crystals, with specific crystalline forms occurring when a mineral’s atoms join in a particular pattern or internal structure. This arrangement is determined by several factors, including the chemistry and structure of the mineral’s atoms, or even the environment in which the crystal grew.

Overall, there are specific angles between corresponding faces of all crystals. Mineralogists (scientists who study minerals) divide these crystalline forms into 32 geometric classes of symmetry; they use this information to identify and classify certain minerals.

The crystals are also subdivided into seven systems on the basis of an imaginary straight line that passes through a crystal’s center (or axis). The seven groups include cubic (or isometric), tetragonal, ortho-rhombic, monoclinic, triclinic, hexagonal, and trigonal (or rhombohedral). For example, a crystal in the cubic system has three axes that intersect at right angles; the axes are also of equal lengths. The best way to envision this crystal is to think of a box with equal sides—or a cube.