What does the term "amorphous" describe in the context of gemstones?

The term "amorphous" refers to materials that do not possess a long-range ordered or regular crystal structure. In the context of gemstones, this means that these stones lack the well-defined geometric patterns typically found in crystalline minerals. Instead, amorphous materials have a disordered arrangement of atoms, which is characteristic of glass or certain types of opal. This lack of a regular structure can influence the physical properties of the gemstone, such as how light interacts with it and its overall appearance.

In contrast, the other options describe features of crystalline materials, which have ordered arrangements of atoms and distinct geometric shapes that define their crystal structure. Thus, understanding that amorphous materials do not fit this model is key to distinguishing them within the broader category of gemstones.