A simulated diamond is any material designed to imitate the appearance of a natural diamond without sharing its chemical composition or crystal structure. These alternatives are engineered to replicate the diamond’s brilliance, fire, and durability. Understanding the composition of these simulants is necessary to differentiate them from genuine diamond materials.
Understanding Diamond Alternatives
The gemstone market features three distinct categories of stones that appear diamond-like, but their origins and material compositions are fundamentally different. Natural diamonds form deep within the Earth over billions of years, consisting of pure carbon crystallized under immense heat and pressure. Lab-grown diamonds are chemically, physically, and optically identical to their natural counterparts, but they are created in a controlled laboratory environment over a period of weeks.
Simulated diamonds make up the third category. These are non-diamond materials that merely mimic the appearance of a diamond. Unlike lab-grown diamonds, simulants do not possess a carbon-based crystal lattice and therefore have different inherent properties, such as hardness and density.
Primary Materials Used in Simulated Diamonds
The most common and affordable material used as a simulant today is Cubic Zirconia, often abbreviated as CZ. This material is a synthesized form of zirconium dioxide (\(\text{ZrO}_2\)), which is stabilized with small amounts of yttrium or calcium oxide to maintain its cubic crystal structure at room temperature. Its popularity stems from its low cost, ease of mass production, and a visual likeness that has made it the market leader since its commercial introduction in the 1970s.
Another prominent material is Moissanite, which is composed of crystalline silicon carbide (\(\text{SiC}\)). Moissanite is distinct due to its superior physical characteristics, including a Mohs hardness of 9.25, second only to diamond. Nearly all Moissanite used in jewelry is grown in a laboratory, as the naturally occurring mineral is extremely rare; its unique silicon and carbon structure gives it exceptional brilliance and fire.
Before the widespread use of Cubic Zirconia, other materials were briefly used as diamond substitutes. One historical simulant was Yttrium Aluminum Garnet (YAG), a synthetic crystal with the chemical formula \(\text{Y}_3\text{Al}_5\text{O}_{12}\). YAG was popular in the 1960s and 1970s until CZ proved more cost-effective and visually convincing. Glass or “paste” was also used historically, though its lack of durability made it a poor long-term imitation.
Optical and Physical Properties
Simulated diamonds achieve their diamond-like appearance by manipulating the physical properties that govern how light interacts with the stone. One of the primary characteristics is the Refractive Index (RI), which measures how much light bends upon entering the material; a diamond has an RI of 2.42. Moissanite has a significantly higher RI, ranging from 2.65 to 2.69, which often results in a more dramatic, almost excessive brilliance compared to a diamond.
Cubic Zirconia has a lower RI of approximately 2.15 to 2.18, meaning it does not reflect light as efficiently as a diamond. Dispersion, commonly referred to as “fire,” is the material’s ability to separate white light into the spectrum of colors. Both Moissanite (0.104) and CZ (0.058-0.066) have a higher dispersion value than diamond (0.044), causing them to display a more obvious rainbow effect.
The material’s durability is measured by its hardness on the Mohs scale, which indicates resistance to scratching. A natural diamond is the benchmark at 10, while Moissanite scores a highly durable 9.25, making it suitable for daily wear. Cubic Zirconia, however, scores between 8 and 8.5, which is sufficient for jewelry but makes it more susceptible to surface abrasion and a resulting loss of luster over time.
Distinguishing Simulated Diamonds From Natural Gems
The most reliable method for distinguishing a simulant from a natural diamond is through specialized testing based on thermal conductivity. Diamonds are exceptional heat conductors, and standard thermal diamond testers work by measuring how quickly the stone disperses heat. Cubic Zirconia is a poor heat conductor, causing the tool to register it as a non-diamond material.
Moissanite is also an excellent thermal conductor, meaning it will often test positive on basic thermal equipment, requiring more sophisticated methods for identification. A key visual difference for Moissanite is its double refraction, an optical property that causes the back facets to appear doubled when viewed under magnification. Diamonds and Cubic Zirconia do not exhibit this effect, as they are singly refractive.
Another practical test involves specific gravity, which is the stone’s density relative to water. Cubic Zirconia is substantially denser than diamond, possessing a specific gravity of 5.6 to 6.0, compared to a diamond’s 3.52. Consequently, a CZ stone of the same size will be noticeably heavier, a difference jewelers can easily detect. The lower hardness of CZ also means it will often show surface wear or small scratches on the facet junctions after a relatively short period of use.