What is a broad gem category based on chemical composition and crystal structure called?

The term that refers to a broad gem category based on chemical composition and crystal structure is "Group." In gemology, a group encompasses minerals that share similar chemical properties and crystalline characteristics. This classification allows for the organization of a wide range of gems that may have different varieties but share a fundamental structure and composition. For example, the garnet group includes several species, such as almandine, pyrope, and spessartine, all of which share the same crystal structure and similar properties.

In contrast, "Species" is more specific and refers to a particular mineral type within that group that has distinct chemical and physical properties. "Variety" refers to different colors or forms of a species, while "Type" is a more general classification that may not necessarily align with the strict chemical criteria used in gemology. Understanding these distinctions is crucial for accurately categorizing and evaluating gemstones.