Moissanite is the best-known diamond simulant of the current era, and the two are easily confused by eye — which is exactly why testers exist. The differences that matter are physical, visual and financial.
Origin and substance
Diamond is native carbon crystallised deep in the earth (or grown in a laboratory). Moissanite is silicon carbide — natural crystals are so rare that jewellery moissanite is essentially always laboratory-created. It is a distinct material, not a fake diamond any more than a ruby is a fake sapphire; both are gems, one simply carries the heritage and scarcity premium.
Hardness, fire and look
Diamond is the hardest natural material (10 on the Mohs scale); moissanite follows at about 9.25 — both stand up to daily wear. Visually, moissanite has higher dispersion, so it throws more coloured fire, especially in larger sizes; diamond’s appeal is its balance of brilliance and white sparkle. To most casual eyes the difference reads as “very sparkly” versus “classic”, and lighting decides who notices what.
Price and testing
A moissanite of the same apparent size costs a small fraction of a diamond of similar quality — the honest reason for its popularity. Thermal diamond testers, the shop standard, can be fooled by moissanite’s thermal conductivity; proper separation needs electrical-conductivity testing or professional instruments. For the trade-side view of simulants and synthetics — including the tester discussion with Presidium — see what tools gemmologists use; the material science is part of gem identification training at JDMIS.