When testing a clear gemstone at home, you're typically dealing with one of four possibilities: natural diamond, lab-grown diamond (which is chemically and physically identical to natural), moissanite (a distinct gemstone valued for its exceptional fire and brilliance), or cubic zirconia and similar simulants that are lower-cost imitations mimicking the look of diamond.
Since lab-grown diamonds are identical to natural diamonds in composition and properties, at-home testing cannot distinguish between those two. What you can do is separate diamond and moissanite from cubic zirconia, and distinguish diamond from moissanite using the right tools.
Note: All of the tools mentioned below (diamond testers, loupes, UV lights) are widely available online from major retailers like Amazon, and higher quality tools generally give more accurate and consistent results.
Dual Thermal and Electrical Conductivity Tester
A thermal conductivity tester (diamond tester pen) is the fastest way to check if a stone is diamond, since diamonds conduct heat extremely well, which sets them apart from cubic zirconia and glass. However, moissanite conducts heat similarly to diamond, so cheaper single-mode testers often misidentify it as diamond. A dual thermal and electrical conductivity tester gives you accurate results:
- Natural and lab-grown diamonds register as diamond
- Moissanite shows a distinct reading due to its electrical conductivity
- Cubic zirconia and other simulants show no conductivity at all
Loupe Inspection, Facet Edges and Double Refraction
A 10× jeweller's loupe can reveal structural differences between stones. Diamonds have razor-sharp facet edges and crisp facet junctions, while moissanite shows double refraction. Look through the crown straight down and you'll often see doubled facet lines due to its crystal structure. Cubic zirconia typically has slightly rounded facet edges and lacks the precision of either diamond or moissanite.
UV Fluorescence (Supporting Clue)
Around one-third of natural diamonds fluoresce blue under UV light, which isn't definitive but can support your other observations. Diamonds may show blue fluorescence, moissanite typically shows little or different fluorescence, and cubic zirconia usually does not fluoresce at all.
When Home Testing Isn't Enough
Home testing has its limits. Officially distinguishing natural from lab-grown diamonds requires advanced spectroscopy equipment, and if you're selling or insuring a piece, you'll need a certified appraisal for accurate valuation. Hallmarks are helpful but not proof, since counterfeit hallmarks are common.
With the right tools, you can confidently separate diamonds, moissanite, and cubic zirconia at home. A dual diamond tester covers most everyday scenarios. Moissanite stands on its own as a premium gemstone, not as a substitute, and lab-grown diamonds are indistinguishable from natural diamonds without professional equipment. For anything beyond the scope of home testing, a qualified gemologist remains the final authority.
Thanks for reading! Jared & Brie
