What is an included diamond crystal that reaches the surface of a cut diamond called?

An included diamond crystal that reaches the surface of a cut diamond is referred to as a "knot." This term specifically describes an inclusion that manifests as a distinctive small crystal or diamond fragment embedded within the surrounding diamond material and extends out to the surface. Knots can impact both the clarity and overall appearance of a diamond.

When a knot occurs, it can create a unique visual element, but it may also affect the gem's durability if the inclusion is extensive or situated in a vulnerable area. Knots are notable inclusions as they indicate the presence of the original material that formed the diamond, showcasing the natural processes that led to its formation.

In contrast, the other terms refer to different types of inclusions or imperfections within diamonds. An inclusion broadly covers any internal or external flaws, such as air bubbles or other crystals, which may not reach the surface. A feather refers specifically to a type of internal fracture that resembles a feather, and a chip is a small break or loss of material from the diamond’s surface, which is distinctly different from a knot that is a crystal inclusion reaching the surface.