Which of the following is a major risk for a gem's clarity rating?

The major risk for a gem's clarity rating lies in the presence of a large unhealed feather. A feather, which is a type of internal inclusion resembling a crack or fracture, can significantly affect a gem’s structural integrity, light performance, and overall value. When a feather is large and unhealed, it implies that the gem is more susceptible to further damage, such as breaks or cracks, which can compromise both its physical durability and aesthetic appeal. This characteristic is particularly impactful because it not only affects the visual quality of the stone but can also lead to questions about its longevity and usability in jewelry.

While other factors like a surface scratch, an internal black spot, or minor cloudiness can affect clarity, they generally do not have the same degree of severity as a large unhealed feather. A scratch might be treatable, and a black spot can sometimes be less noticeable depending on its position and size, while minor cloudiness often does not significantly impact either visual appearance or durability in the same way a large feather can. Thus, the presence of a large unhealed feather poses the greatest risk and has the most substantial implications for a gem's clarity rating.