The Diamond's Doppelgänger: Why Moissanite Fools Everything But Heat

In 1893, the Nobel Prize-winning chemist Dr. Henri Moissan was investigating fragments of a meteorite that had carved the massive Diablo Canyon crater into the Arizona desert. Amidst the iron and rock, he discovered tiny, glittering crystals. Convinced he had found a new source of diamonds, he was ecstatic. It was only years later, in 1904, that he correctly identified the crystals not as carbon, but as silicon carbide (SiC)—a mineral never before seen in nature. He had discovered a stone literally born from the stars.

That celestial origin story is the perfect beginning for moissanite, a gemstone that would go on to become the most brilliant and deceptive diamond doppelgänger the world has ever known. It is so convincing that it can fool jewelers, pawn brokers, and even the electronic testers designed to sniff out fakes. There is, however, one physical property it cannot imitate, one test it cannot pass. To understand its secret, you have to understand the art of its deception.

Act I: The Perfect Impostor

Natural moissanite is rarer than diamond. The glittering fragments from Dr. Moissan’s meteorite are virtually all that exists. But in the late 20th century, scientists perfected a method to grow large, flawless silicon carbide crystals in a lab. When this lab-grown moissanite was cut and faceted, the jewelry world was stunned.

It was impossibly brilliant. Moissanite boasts a higher refractive index than diamond, meaning it bends light more effectively. More impressively, its “fire,” or dispersion, is more than double that of a diamond (0.104 vs. 0.044). This gives it a spectacular, fiery rainbow flash that many find captivating. It’s also incredibly tough, scoring a 9.25 on the Mohs hardness scale, second only to diamond’s perfect 10. It was harder and more brilliant than any previous diamond simulant, like Cubic Zirconia (CZ). This wasn’t just a good imitation; it was a magnificent gemstone in its own right. But its similarity to diamond was its most challenging trait.

Act II: The Deception

In the jewelry trade, a common tool for quick diamond verification is the “diamond tester pen.” Most of these affordable, pen-sized devices don’t test for heat, but for electrical conductivity.

This test works because most diamonds (specifically Type IIa, which are the most chemically pure) are excellent electrical insulators. They do not conduct electricity. Many simulants, like CZ, are also insulators. So, a simple pen that tests for electrical conductivity can effectively separate diamond from many of its fakes. If the pen’s tip touches a stone and no current flows, it beeps “Diamond.”

But moissanite is different. Silicon carbide is a semiconductor. This means it conducts electricity, albeit not as well as a metal. When the tip of a standard electrical diamond tester touches moissanite, a current flows. The device, designed with a simple “conducts/doesn’t conduct” logic, is fooled. It reads the electrical current and confidently beeps, signaling “Diamond.” This single property allowed moissanite to slip past the industry’s first line of defense, creating confusion and earning it a reputation as a master of disguise.

Act III: The Unmasking by Heat

If electricity can be fooled, gemologists needed a more fundamental property to distinguish these two stones. They found it not in the flow of electrons, but in the flow of heat. As we’ve explored, diamond is a thermal superman, conducting heat with unparalleled efficiency (around 2200 W/m·K). This is its most extreme and unique physical characteristic.

Moissanite, while an excellent thermal conductor in its own right, simply cannot compete. Its thermal conductivity is significantly lower, clocking in at around 300-490 W/m·K depending on its quality. It’s still a fantastic conductor—far better than any other simulant like glass (1 W/m·K) or CZ (around 8 W/m·K)—but it exists in a different league than diamond.

This substantial gap in thermal conductivity is the key. A device designed to measure this property, like the Presidium Gem Tester II, cannot be fooled.

When its heated probe touches a stone, it measures the rate of heat loss. * On a Diamond: The heat drains away almost instantly. The tester registers this massive heat loss and indicates “Diamond.” * On a Moissanite: The heat drains away quickly, but noticeably slower than from a diamond. The tester registers this specific rate of heat loss and indicates “Moissanite” on its calibrated scale. * On Glass or CZ: The heat barely moves. The tester registers negligible heat loss and the needle stays in the low range.

The thermal tester doesn’t care about electrical properties. It reads a fundamental physical signature that moissanite, for all its brilliance, cannot fake. It is the definitive, on-the-spot test to settle the diamond vs. moissanite question.

Two Stones, Two Stories

It’s a mistake to think of moissanite as a “fake” diamond. It is a unique gemstone with its own origin story, its own stunning properties, and its own place in the market. It is not trying to be diamond; it is simply moissanite, a stone born of stars and perfected by science.

The challenge it presents to the jewelry world is one of identification, not authenticity. And in that challenge, we see the beauty of science. Where one test fails, another, based on a different physical principle, succeeds. The story of moissanite and diamond is a perfect illustration of why in gemology, as in life, looking at a problem from a new perspective can reveal the truth that was hiding in plain sight all along.