Feature Gems & Gemology, Fall 1996, Vol. 32, No. 3

Introduction to Analyzing Internal Growth Structures: Identification of the Negative d Plane in Natural Ruby

Growth-structure analysis has become increasingly important as a gemological tool for locality classification and distinguishing between natural and synthetic gemstones. This article presents the methods and instruments needed to analyze the internal growth structures of corundum. As an application of this testing procedure, the negative rhombohedral d (0112) plane is documented as part of the crystal habit in a small number of natural rubies—both as a subordinate form and, for the first time in natural rubies, as a dominant crystal form. Until recently, this crystal face was primarily associated with flux-grown synthetic rubies and sapphires.