Final answer:
The correct answer is D. natural which refers to features of a gemstone left from its original rough state, showing its authenticity.
Step-by-step explanation:
In geology and gemology, the term "natural" refers to a distinctive surface indentation on a precious stone, typically characterized by tiny, root-like feathers penetrating the stone. This phenomenon is a visible testament to the gem's raw or uncut state, showcasing marks and features that have not been entirely polished away during the cutting and finishing processes. Naturals serve as authenticating features, providing evidence that the stone retains elements of its original rough surface.
The concept of naturals is analogous to the root structure observed in plant biology. In the context of gemology, these root-like feathers are intricate markings within the stone, often resembling the delicate and branching nature of actual roots in plant biology. These features are preserved, deliberately or incidentally, during the stone's cutting and polishing stages.
Similar to the thin, tubular, and sometimes branching structure formed by the filling of a hole left by a root in plant biology, naturals in gemology offer a unique and genuine characteristic. They become identifiers of authenticity, revealing that the gem has not undergone excessive alteration or artificial enhancements. The presence of naturals in a precious stone serves as a connection to its geological origins and provides a visual narrative of its journey from its raw, uncut form to its refined, yet authentically marked, polished state.