By Lauriane Lognay

Have you ever wondered if there was any rhyme or reason to the structure of rough gemstones, or how can geologists and gemmologists can differentiate one crystal rough from another? Well, wonder no more! This article discusses the differences between crystal systems, as well as ways jewellery professionals can expertly tell them apart.

First thing first, though: What is a crystalline structure? Simply put, this is a regular or repeated, three-dimensional arrangement of bonded atoms which come together to create a specific formation (i.e. rough mineral). The classification of crystals into their systems is based on their shape, symmetry, morphology, appearance, and similarities in physical properties.

There is some debate about the exact number of crystal systems—mainly because some are quite similar. However, for the sake of representing the whole, we will discuss all eight systems commonly considered:

1. Cubic
2. Hexagonal
3. Quadratic
4. Orthorhombic
5. Monoclinic
6. Rhombohedral
7. Triclinic
8. Amorphous

While No. 8 (amorphous) is a system which does not contain any crystalline structure, it is, nonetheless, an important category. Amorphous stones are composed largely of atoms, molecules, or tiny crystalline parts, oriented in random ways. As such, these take no specific crystalline shape.

The eight crystal systems cover all the precious and semi-precious stones used and known in the fields of jewellery, gemmology, and lapidary. Once you have memorized it, you will find it much easier to identify each mineral.