The term used for imperfectly formed diamonds that have visible growth lines is?

The term used for imperfectly formed diamonds that exhibit visible growth lines is "growth-marked diamonds." This designation refers specifically to those diamonds that have characteristics indicative of their natural formation process, including lines or patterns formed as the diamond crystallizes. These growth lines can be significant in gemology, as they provide insights into the formation environment and conditions of the diamond.

Understanding the visible patterns and growth lines is crucial for gemologists and can affect a diamond's overall classification and value. Growth-marked diamonds can appear less desirable in some markets due to their imperfections, yet they also carry historical and geological significance that can be appreciated by collectors and professionals.

In contrast, the other terms do not accurately describe diamonds with visible growth lines. "Fancy diamonds" are typically understood to be colored diamonds and do not necessarily relate to growth imperfections. "Glassie diamonds" might refer to diamonds with a specific appearance or clarity but wouldn’t denote their growth characteristics. "Rough diamonds" refer to uncut, unpolished diamonds and don’t specifically address the presence of growth lines. Thus, "growth-marked diamonds" is the most appropriate and precise term in this context.