The Complete Moissanite Science Guide: Silicon Carbide, Hardness, Optics & Durability

This is our comprehensive scientific reference for moissanite — written by our gemology team for buyers who want to understand not just what moissanite looks like, but what it actually is at a material level. We cover everything from crystal chemistry to optical physics to long-term durability behavior.

Part 1: What Moissanite Is — The Material Science

Chemical Composition

Moissanite is silicon carbide (SiC) — a compound of silicon and carbon in a 1:1 atomic ratio. First discovered in 1893 by Dr. Henri Moissan in a meteorite crater in Arizona. Natural gem-quality moissanite is extraordinarily rare; virtually all moissanite used in jewelry today is lab-created.

Crystal Structure

Silicon carbide exists in over 250 polytypes. Gem-quality jewelry moissanite uses 6H-SiC (α-SiC), which produces the optical properties closest to diamond. This structure causes moissanite's birefringence (double refraction) — distinguishing it from diamond at the crystal physics level.

How Lab Moissanite Is Made

Produced via physical vapor transport (PVT) at temperatures exceeding 2,000°C. Silicon and carbon vapors deposit onto a seed crystal over several weeks. The resulting SiC boule is then cut and faceted using diamond-grade equipment.

→ Identification implications: Can a Jeweler Tell Moissanite from Diamond Without Equipment?

Part 2: Physical Properties

Hardness: 9.25 Mohs

Second hardest gemstone material after diamond (10). Moissanite cannot be scratched by any material encountered in daily life — only diamond or other moissanite can scratch it.

Specific Gravity: 3.21 g/cm³

~10% less dense than diamond (3.52). This is why same-carat moissanite is physically larger than diamond — and why DEW (diamond equivalent weight) is the standard for comparison.

Toughness: Excellent

Moissanite has no cleavage planes, making it more fracture-resistant than diamond despite being slightly softer. Diamond can fracture along its cleavage under a sharp blow; moissanite cannot.

→ Can Moissanite Get Scratched? The Mohs Scale Explained

Part 3: Optical Properties

Refractive Index: 2.65–2.69

Highest RI of any gemstone commonly used in jewelry — ~10% higher than diamond's 2.42. This is the primary cause of moissanite's superior brilliance. The range exists because moissanite is doubly refractive (two RI values depending on light polarization).

Dispersion: 0.104

2.4× higher than diamond's 0.044. This produces moissanite's distinctive rainbow fire — measurably more intense than diamond, especially in direct or point-source lighting.

→ Why Does Moissanite Look More Brilliant Than Diamond?

Birefringence: 0.043

Moissanite splits light into two rays (birefringent). Diamond is singly refractive (birefringence = 0). Under 10× loupe, this produces visible back-facet doubling — the most reliable non-electronic identification method.

UV Fluorescence

Weak–moderate orange/yellowish-green under longwave UV (365nm). Characteristic of 6H-SiC. No visible effect under normal wear conditions.

→ What Happens to Moissanite Under UV Light?

Luster: Adamantine

Same classification as diamond — the highest luster category for gemstones. Produces the bright mirror-like surface reflection characteristic of both stones.

Part 4: Thermal Properties

Thermal Conductivity: 120–490 W/(m·K)

Exceptionally high for a non-diamond material. This is why standard thermal diamond testers register moissanite as diamond — they detect high thermal conductivity, and moissanite's exceeds their threshold. A dual-mode tester is required for reliable electronic identification.

→ Does Moissanite Pass a Thermal Diamond Tester?

Melting Point: >2,700°C

Will not be damaged by jeweler's torch work during sizing or repair — an advantage over heat-sensitive stones like opal or tanzanite.

Part 5: Long-Term Durability

Silicon carbide is chemically stable under all conditions encountered in jewelry wear. Moissanite does not:

• Lose brilliance or fire with age (optical properties are intrinsic to crystal structure, not a coating)
• Become cloudy from normal chemical exposure
• Develop fractures from thermal cycling in daily wear
• React with skin chemistry or standard cleaning products

→ Is Moissanite Good for Everyday Wear?
→ How Long Does Moissanite Last? Lifetime Durability Breakdown

Complete Property Reference

Related Reading

• Moissanite Grading vs. Diamond Grading: Why the Standards Are Different
• What Happens to Moissanite Under UV Light?
• Can a Jeweler Tell Moissanite from Diamond Without Equipment?
• The Science of Brilliance: Silicon Carbide
• Is Moissanite a Real Gemstone?
• Meet Our Gemology Experts at Moissanite Shine