Moissanite Double Refraction Explained

Moissanite cut diagram

Have you ever closely examined a moissanite gemstone and noticed a subtle doubling effect? As an optically anisotropic material, moissanite exhibits a phenomenon known as birefringence, or double refraction. But what exactly causes this, and should it impact your moissanite buying decision?

In this guide, I‘ll provide an in-depth look at the science behind moissanite‘s double refraction. You‘ll learn about the unique structure of moissanite crystals, how precisely cutting the gems minimizes visible doubling, and why moissanite can rival diamonds in brilliance and fire despite this optical trait. Let‘s explore the fascinating physics and geology behind one of today‘s most popular diamond alternatives!

Where Does Moissanite Come From?

First, a quick primer on what moissanite is and where it originates from. Moissanite is the mineral form of silicon carbide (SiC). It was first discovered in 1893 by Nobel Prize-winning chemist Dr. Henri Moissan, who later named the mineral after himself. He stumbled upon microscopic particles of the incredibly rare material in a meteor crater in Arizona.

Since natural moissanite deposits on Earth are virtually non-existent, almost all moissanite used in jewelry is lab-created. High-tech manufacturing processes can grow near-flawless moissanite crystals in a controlled laboratory environment. This allows for sustainable, ethical production of this unique diamond alternative.

So despite being discovered in a meteor, moissanite used in rings and pendants today is scientifically engineered right here on Earth! Now let‘s examine why this space-born mineral has such unusual optical abilities.

How Moissanite‘s Structure Causes Double Refraction

Moissanite possesses special optical properties due to its distinct atomic makeup. To understand where double refraction comes from, we need to look at the microscopic level of the crystal lattice.

The basic building block of moissanite is carbon and silicon atoms bonded together into a repeatable 3-dimensional pattern. The specific arrangement of these atoms gives moissanite its defining characteristics.

Moissanite crystallizes in the hexagonal crystal system, meaning the shape of the crystal lattice is based on hexagons. Importantly, the structure is asymmetrical because the atoms are ordered differently along the vertical c-axis compared to the horizontal directions.

Meanwhile, diamond has a cubic crystal system, where the atoms are arranged identically along all axes. This gives diamond a fully symmetrical lattice.

The table below summarizes the differences between symmetrical cubic systems like diamond, and asymmetrical hexagonal systems like moissanite:

Isotropic Material (Diamond) Anisotropic Material (Moissanite)
Cubic crystal system Hexagonal crystal system
Optically symmetrical Optically asymmetrical
Does not cause double refraction Causes double refraction

This asymmetry in moissanite‘s lattice causes it to behave differently along the c-axis compared to other directions. This variable, angle-dependent behavior is called anisotropy. It allows moissanite to unusually bend light in certain directions, like splitting it into two separate rays aka double refraction.

So in summary, the mismatch in symmetries between cubic diamond and hexagonal moissanite produces very different interactions with light. Next we‘ll explore exactly what happens when light encounters the uncommon hexagonal lattice.

Splitting Light Rays Through the Crystal

When an incoming beam of ordinary unpolarized light strikes the asymmetrical moissanite crystal, it splits into two new polarized light rays: the ordinary ray (O-ray) and extraordinary ray (E-ray).

Moissanite double refraction diagram

The O-ray follows the classic laws of refraction – it bends at an angle predicted by the refractive indexes of the materials. But the E-ray does not obey these rules and refracts at a completely different angle. This is because the E-ray encounters a different refractive index across the asymmetric hexagonal lattice.

Having two polarized rays travel through the crystal creates birefringence – the ordinary and extraordinary rays move at different velocities and take different paths. Where the light rays overlap upon exiting, interference patterns occur which we observe as doubling or blurring. This is most exaggerated when viewing from the side.

Interestingly, physicists can calculate exactly how the light will split in moissanite based on principles like Snell‘s Law and the Optical Indicatrix concept. The key point is that light behaves predictably based on the crystal‘s orientation – but in more complex ways than a cubic material.

To learn more on the optical physics, I spoke with research physicist Dr. Michael Raines who studies crystal optics:

"Moissanite provides an excellent demonstration of light interacting with an anisotropic structure. The splitting of light rays is not random, but follows mathematical models based on the crystal lattice symmetry. There is still much to discover about controlling and engineering these optical phenomena in useful ways."

While complex under the surface, this optical splitting manifests as breathtaking flashes of rainbow-hued light to our eyes.

Precision Cutting is Key

Now that we understand why moissanite‘s atomic structure causes double refraction, how can jewelers minimize this effect? The secret lies in precision cutting.

When a moissanite rough gem is cut, the orientation of the crystal lattice matters immensely. Cutters must carefully study the optic direction called the c-axis to determine the best positioning that controls double refraction.

Ideally, the moissanite is cut so that the c-axis runs straight from the apex of the gem down through the point or table facet. In jewelry terminology, this direction perpendicular to the table is called the optic axis.

Cutting moissanite along the optic axis makes it behave essentially like a singly refractive gem when viewing the table facet. This means refraction of light entering the crown is minimized rather than splitting into two rays.

Moissanite cut diagram

Master gem cutters use specialized tools like refractive index fluid and optical microscopes to map out the ideal cut orientation. While challenging, optimizing for double refraction results in maximum sparkle.

Charles & Colvard, a top moissanite brand, even developed a patent-pending cut called Hearts & Arrows that masks double refraction. This technique aligns mirrored patterns across key parts of the gem for perfect symmetry.

So while physics gives moissanite an extra optical complexity, human ingenuity provides innovative solutions!

Observing Moissanite‘s Double Refraction

How can you observe this hidden doubling effect as a jewelry owner? Under normal wear, the precision cutting conceals any doubling. But with close inspection from certain angles, you can witness this optical phenomenon.

To see double refraction in moissanite:

  • Examine near the table while tilting the gem from side to side. Slight blurring may be visible along facet junctions as you rotate.

  • Turn the moissanite on its side and look through the table horizontally to exaggerate the split rays.

  • Use a polariscope or other optical device to clearly separate the ordinary and extraordinary rays.

The key is knowing what vantage points make the double refraction apparent. When light passes straight down the optic axis of a well-cut moissanite, the doubling remains imperceptible.

Double Refraction Myths vs. Facts

Despite expert cutting techniques to minimize its visibility, misconceptions still surround moissanite’s double refraction. Let’s separate some common myths from the facts:

Myth: All moissanite looks blurry and lacks fire.

Fact: Precision cuts like Hearts & Arrows display exceptional brilliance and flash. Well-aligned moissanite exhibits no visible doubling face-up.

Myth: Moissanite‘s doubling means it‘s poorly manufactured.

Fact: The double refraction comes from moissanite‘s innate crystal structure, not production flaws. It‘s a natural optical property.

Myth: Moissanite has a higher refractive index so more doubling.

Fact: Diamond and moissanite have nearly equal refractive indexes typically between 2.4-2.7. Neither is clearly higher.

Myth: Orienting moissanite to minimize double refraction harms durability.

Fact: Cutting along the optic axis does not impact moissanite’s excellent hardness or toughness. This axis orientation is solely an optical consideration.

The reality is that moissanite’s fiery brilliance outpaces many gems. And with such similar optics to diamond, double refraction should not deter you from choosing this sustainable alternative.

Should Double Refraction Affect Your Moissanite Buying Decision?

At this point, you may be wondering if moissanite’s double refraction should give you pause around durability or appearance. After diving into the physics behind this optical effect, I can confidently say double refraction is not a reason to avoid moissanite.

Here are the key takeaways around moissanite’s doubly refractive properties:

  • It originates from the innate asymmetry in moissanite’s crystal structure, not any manufacturing flaws.

  • Well-cut moissanite has double refraction rendered nearly invisible face-up.

  • Observed from certain angles, some doubling along facets can be detected upon close inspection. But this requires carefully controlled lighting and viewing.

  • Moissanite scores top ratings for brilliance, fire, and scintillation compared to other transparent gems. Double refraction does not diminish its optical performance.

  • Durability is not impacted; hardness, toughness, and brilliance over time are uncompromised by this optical trait.

While an inherent material property, double refraction has been extensively studied and accounted for by moissanite cutters. The jewel‘s dazzling light display remains uncompromised. So let your aesthetic tastes, not misplaced optical concerns, guide your gemstone buying decisions.

The Takeaway on Moissanite and Double Refraction

I hope this deep dive dispelled any negative perceptions around moissanite’s doubly refractive abilities. While sounding complex, this optical effect stems from fascinating physics we can control and minimize through clever gem cutting. When a light ray passes through a precisely aligned moissanite, the beauty of its atomic structure is unveiled as wondrous flashes of color.

Understanding the science behind moissanite’s brilliant display can help you appreciate the natural wonders that underpin its allure. If you’re looking for an eco-friendly diamond alternative that captures light with extra dimension, don’t let double refraction deter you. Moissanite remains one of the most dazzling, sustainable options available today.

Related Resources:

Gemological Institute of America – Moissanite Guide:

Rapaport Diamond Education – Birefringence:

International Gem Society – Anisotropy in Gemstones:

Written by Jason Striegel

C/C++, Java, Python, Linux developer for 18 years, A-Tech enthusiast love to share some useful tech hacks.