You recently started browsing for engagement rings and are in awe with all of the shimmering options. If some gems look more sparkly than others, you’re not imagining it. Certain stones score higher on the brilliance refractive index and therefore sparkle more. What is this index and how does it affect the rings you’re seeing? We’re here to tell you!

What is Diamond Brilliance?

Before we dig into the index, let’s explain some related concepts. When we say “brilliance,” we’re essentially referring to a gemstone’s sparkle/brightness, which is created when light enters a diamond through the top, flat surface and gets reflected back through it.

How is a diamond able to reflect different flashes of color and white light? The simple answer is a gem’s cut — the arrangement and proportion of its flat, polished surfaces (aka facets). When light hits a stone, it bounces off of the many surfaces, resulting in beautiful, colorful beams. However, keep in mind that facets are positioned differently in each gem, which ultimately impacts a stone’s shimmer. If these facets are poorly arranged, a diamond will display less sheen.

What is the Brilliance Refractive Index?

Now that you understand the sparkle basics, how does the brilliance refractive index fit in? This index calculates how much a gem decreases, bends and reflects light as it enters a stone. It basically assigns a value to the gem’s sparkle, so you can more easily compare which stones shine brighter.

What does all of that mean? When light hits a clear gem, such as a diamond, its speed drops. That’s because the gem is a denser object than air, the medium through which light was just traveling. The reduced speed causes light to enter a diamond at different angles. Therefore, light might not flow through the stone in an ideal path and be reflected properly off of the facets.

According to the University of Texas at Austin, the following formula can be used to calculate the refractive index. Measured stones receive scores between 1.2 and roughly 3, and gems with higher scores are more brilliant.

R.I. = velocity of light in air

velocity of light in gem

Which Gems are Most Brilliant?

You’re probably already thinking about diamonds, as they’re clear, colorless and popular among engaged couples. Diamonds certainly are brilliant, scoring a 2.42 on the index. For reference, emeralds range between 1.56 and 1.60, while rubies and sapphires hover around 1.76.

However, diamonds aren’t the most brilliant gem. Surprisingly, the title goes to diamond alternative moissanite. That means this stone reflects light better than diamonds, scoring between 2.65 and 2.69 on the brilliance refractive index. Learn more about this durable, silicon carbide stone here.

Have a question? We can help!

Gage Diamonds is Chicago's premier jewelry showroom and online retailer of engagement rings, wedding bands, and fine jewelry. We offer a selection of dazzling handpicked diamonds, including certified natural and lab grown diamonds, as well as moissanites.

We’re committed to helping you find the ring of your dreams. For inspiration, browse our selection of natural and lab grown diamonds, or set up an appointment with a member of our trusted staff at our in-person showroom.

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