Which term describes a family of gems from several closely related mineral species?

The term that describes a family of gems from several closely related mineral species is "Group." In the context of gemstones, a group refers to a classification that encompasses multiple minerals that share a similar chemical composition and crystalline structure. These minerals typically exhibit common properties and characteristics, making them related in various ways.

For instance, the garnet group includes several different species like almandine, pyrope, and spessartine, all of which are structurally similar but differ in their specific chemical compositions. Using the term "group" effectively conveys the idea of these minerals' interconnectedness due to their shared traits.

In contrast, other terms like "stratum," "class," and "collection" do not accurately capture this specific relationship among related mineral species. "Stratum" generally refers to layers of meaning or geological deposits, "class" might refer to a broader category without emphasizing the closeness of the minerals, and "collection" usually indicates a curated group of items rather than a scientifically classified family of minerals. Thus, "Group" is the most precise term for describing this close relationship among related gemstone species.