Which of the following describes the chemical composition of gem species?

The correct answer focuses on the broad category that encompasses various structures and compounds that can define gem species. Gem species are typically categorized based on their chemical composition and crystal structure, which can include a range of elements and compounds. For example, diamond is identified as a species composed entirely of carbon, while other gems, like beryl, may contain a combination of beryllium, aluminium, silicon, and oxygen, among other elements.

Understanding gem species through their chemical makeup allows gemologists to classify and differentiate between them based on their unique properties. This classification is essential for identifying gems, determining their characteristics, and understanding their formation processes.

In contrast, other options focus on aspects not related to the chemical composition. Precise measurements of a gem's cut pertain to its proportions and symmetry rather than its material makeup. Classification by origin may consider where a gem was mined or sourced but does not encompass its chemical structure. Finally, representations of market price relate to economic value rather than scientific classification. Thus, the focus on the broad category of structures and compounds accurately captures the essence of what comprises gem species.