Most gemstone buyers know moissanite as a brilliant, durable stone — but very few know what it actually is at the atomic level. Understanding moissanite’s chemical composition explains every property that makes it exceptional: its hardness, its fire, its thermal conductivity, and its long-term stability.
The Chemical Formula: SiC
Moissanite is silicon carbide, with the chemical formula SiC. Each molecule consists of one silicon atom (Si) bonded to one carbon atom (C) in a covalent bond — one of the strongest chemical bonds in nature. In a covalent bond, atoms share electrons rather than transferring them, producing a highly stable, non-ionic compound. This is the same type of bonding found in diamond (pure carbon, C), which is why both materials share exceptional hardness and thermal conductivity despite having different compositions.
Silicon Carbide in Nature and in the Lab
Natural silicon carbide is extraordinarily rare — it was first discovered in 1893 by Henri Moissan in a meteorite crater in Arizona, which is why the gemstone bears his name. Natural moissanite crystals exist in quantities too small to be used in jewelry. All moissanite used in fine jewelry today is laboratory-grown silicon carbide, produced through controlled high-temperature crystal growth processes. The compound is chemically identical to natural moissanite — same formula (SiC), same crystal structure, same properties.
The Covalent Bond: Why SiC Is So Hard
Diamond’s extreme hardness (Mohs 10) comes from its covalent carbon-carbon (C–C) bonds arranged in a tetrahedral crystal lattice. Moissanite’s silicon-carbon (Si–C) bond is similarly covalent and similarly strong. The Si–C bond length is approximately 1.89 Ångströms — slightly longer than the C–C bond in diamond (1.54 Å), which is why moissanite scores 9.25 on the Mohs scale rather than 10. The covalent Si–C network extends throughout the crystal in all directions, with no weak ionic planes — this is the structural source of moissanite’s exceptional fracture toughness (7.6 MPa·m½). See our toughness vs. hardness guide and Mohs hardness guide.
Atomic Mass and Molar Composition
Silicon (Si) has an atomic mass of approximately 28.09 g/mol. Carbon (C) has an atomic mass of approximately 12.01 g/mol. The molar mass of SiC is therefore approximately 40.10 g/mol. By mass percentage: silicon constitutes ~70% of SiC by weight and carbon ~30%. This composition — heavier silicon paired with lighter carbon — produces moissanite’s specific gravity of 3.21 g/cm³, compared to diamond’s 3.51 g/cm³. This is why a moissanite stone is approximately 8.5% lighter than a diamond of the same millimeter dimensions — relevant for buyers comparing carat weight to visual size. See our specific gravity guide.
How SiC Produces Moissanite’s Optical Properties
The SiC compound’s electron structure determines how it interacts with light. The refractive index of moissanite (2.65–2.69) is higher than diamond’s (2.42), meaning light bends more sharply as it enters the stone — producing greater white brilliance. The dispersion coefficient of SiC (0.104) is 2.4 times higher than diamond’s (0.044), meaning SiC separates white light into spectral colors more effectively — producing moissanite’s distinctive rainbow fire. These are direct consequences of silicon carbide’s specific electron density and bond polarizability. See our refractive index guide and dispersion guide.
Thermal Properties of SiC
Silicon carbide has a thermal conductivity of approximately 120–490 W/m·K depending on polytype and crystal purity — within the same range as diamond (900–2,320 W/m·K for Type IIa). This high thermal conductivity is why moissanite causes thermal diamond testers to react positively: both materials conduct heat rapidly away from the probe tip. The SiC compound also has a high melting point of approximately 2,730°C (4,946°F) under atmospheric pressure, contributing to its exceptional thermal stability for daily jewelry wear. See our thermal conductivity guide.
SiC vs. Diamond vs. CZ: The Chemical Comparison
Diamond (C): Pure carbon in a cubic crystal lattice. Mohs 10, specific gravity 3.51, refractive index 2.42, dispersion 0.044.
Moissanite (SiC): Silicon carbide in a hexagonal crystal lattice. Mohs 9.25, specific gravity 3.21, refractive index 2.65–2.69, dispersion 0.104.
Cubic Zirconia (ZrO₂): Zirconium dioxide in a cubic lattice. Mohs 8–8.5, specific gravity 5.6–6.0, refractive index 2.15–2.18, dispersion 0.060.
Moissanite and diamond share covalent bonding and high hardness. CZ is an ionic compound — fundamentally different chemistry, much lower hardness, and significantly higher density. See our full CZ vs. moissanite comparison.
What SiC Means for Buyers
Understanding that moissanite is silicon carbide — not a diamond copy, not a simulant, but a distinct mineral compound — reframes the buying decision entirely. SiC’s covalent bond structure produces properties that are not inferior to diamond but are often superior: higher fire, greater fracture toughness, no cleavage planes, and equivalent scratch resistance for all practical daily wear purposes. The stone’s performance is a direct result of its chemistry — not marketing.
Shop DEF/VVS1 Moissanite
Rings · Earrings · Necklaces · Bracelets. DEF, VVS1, GRA certified, solid gold, lifetime warranty, free US shipping.