Final answer:
The bottom-most facet of a gemstone is called the culet, which helps to protect the tip of the gem and can influence the stone's appearance and durability.
Step-by-step explanation:
The bottom-most facet of a gemstone is called the culet. This small facet can be found at the very bottom of a gem and its main purpose is to protect the tip of the gem from being chipped or damaged. In some gemstone cuts, the culet is a point rather than a facet. The size and quality of the culet can affect the overall appearance and sparkle of the gemstone, as well as its durability. For example, a larger culet can be seen through the top of the gemstone, potentially impacting its brilliance and clarity.