Moissanite vs lab diamond
Moissanite is silicon carbide, a stone in its own right, grown in a lab, harder than sapphire, with more rainbow fire than diamond and a price that makes a 2 carat pair of studs a lunch-money purchase. Lab diamond is diamond, carbon, grown by HPHT or CVD, identical to mined diamond in every physical way and graded on the same scale. If you want the real thing, buy lab diamond. If you want the biggest, flashiest white stone for the least money and do not care what it is called, buy moissanite. Every pair of studs and the pendant we ordered are moissanite; the loose melee is lab diamond.
What each one is
Moissanite occurs in nature only in meteorite traces; every gem you can buy is grown. It has a higher refractive index than diamond (about 2.65 against 2.42) and much higher dispersion, which is the rainbow flash. Lab diamond is chemically, optically and physically diamond; the only differences are growth marks a laboratory can read, and the price.
The grades on the listing
Amazon moissanite listings borrow the diamond scale: D colour, VVS1 clarity. There is no industry body grading moissanite the way GIA grades diamond; a GRA card, which some listings include, is a report from a private lab stating that the stone is moissanite and giving its grade. Treat it as confirmation of species, not as a quality guarantee. On lab diamond, a report from IGI or GIA with a girdle inscription is what a grade means; melee and stones under about 0.3 carat are sold ungraded by everyone.
Telling them apart
A thermal diamond tester reads both as diamond. An electrical tester separates them: moissanite conducts, diamond does not. Under a loupe, moissanite is doubly refractive, so the back facets look doubled when you look through the stone at an angle; diamond is singly refractive and the facets look crisp. Combined testers cost less than a pair of the studs on this site and settle it in seconds.
Which to buy
- Studs and pendants you will wear hard and not think about: moissanite. The stone will outlast the plating on the silver it is set in.
- An engagement stone or anything you want to be diamond: lab diamond with an IGI or GIA report. Ungraded lab diamond over half a carat is a bad bet from an anonymous seller.
- Accent and pave stones for a setting: lab diamond melee, because it is now cheap enough and it is the real thing under a loupe.
Frequently Asked Questions
Will moissanite pass a diamond tester?
A thermal tester, yes: moissanite conducts heat like diamond and reads as diamond. An electrical tester or a combined tester separates them, because moissanite conducts electricity and diamond does not. Jewellers use the combined kind for this reason.
Does moissanite look fake?
In sunlight a large moissanite throws more rainbow flash than a diamond, which some people love and some read as too much. Under a carat, most people cannot tell. Colour has improved: older moissanite had a green or yellow tint; current stones sold as D to F colour are near colourless.
Which is harder?
Diamond, at 10 on the Mohs scale; moissanite is 9.25, harder than sapphire at 9. Both scratch glass and shrug off daily wear; both can chip on a hard knock at a thin girdle.