On The Fly

Over the course of a career teaching gemology, students have asked me many questions that gemologists tend to take for granted. This hit home recently at a writers group meeting when I casually used the term refractive index in one of my fictional works and the question immediately came up, “What is refractive index?” This brief column is devoted to you, the curious student. It is an opportunity to ask anything you ever wanted to know about gemology (within reason) but were afraid to ask. So let’s begin. What does refractive index (R.I.) mean? Gem-A Refractometer The amount to which a gem slows light is called its refractive index (R.I.). R.I. is calculated by the ratio of the speed of light in air to its speed in a gem. It is one of the measurable properties that gemologists use to assist with a gemstone’s identification.  For example, using your smartphone or computer, go to the computational database WolframAlpha . Type in “What is the speed of light in air?...