corundum, Canada.12, gems

Peterson discusses black star corundum, a dark variety of corundum that displays asterism when cut en cabochon. The article describes the appearance and gemological characteristics of the material and the inclusions responsible for the star effect, produced by oriented needle-like inclusions that reflect light along crystallographically controlled directions. It considers the relationship between the dark body color, inclusions, and visibility of the star, as well as the orientation required in cutting to display the phenomenon effectively. The brief account provides a practical description of black star corundum and the optical phenomenon responsible for its distinctive appearance.