What you are actually looking at.
Natural diamond
- What it is
- Carbon crystallised over geological time
- The giveaway
- Crisp white sparkle with restrained colour flashes
Lab grown diamond
- What it is
- Chemically identical diamond, grown in weeks
- The giveaway
- None visible. This one genuinely needs equipment.
Moissanite
- What it is
- Silicon carbide
- The giveaway
- Too much fire. Rainbow flashes that read almost disco under light.
Cubic zirconia
- What it is
- Zirconium dioxide
- The giveaway
- Glassy and lifeless, and it scratches and clouds with wear.
The single most important thing on this page: a handheld diamond tester measures thermal conductivity, and moissanite conducts similarly enough that cheap testers read it as diamond. Testers that also check electrical conductivity separate the two. Neither kind can identify a lab grown stone.
Tests that actually tell you something.
- 01
The newspaper test
Place a loose stone flat side down on printed text. A round brilliant diamond bends light so severely you cannot read through it. Read the letters clearly and you are probably looking at glass or a poorly cut CZ. Only works on loose stones.
- 02
Look at the sparkle character
Hold it under a single light and turn it. Diamond throws mostly white light with occasional colour. Moissanite throws rainbows constantly. Once you have seen them side by side you cannot unsee it.
- 03
Check the girdle under magnification
Many natural diamonds have a faintly frosted or facetted girdle, and lab stones are often laser inscribed there with a report number. Phone camera at full zoom will sometimes catch it.
- 04
Inspect for wear
Diamond is the hardest natural material and its facet edges stay razor sharp for decades. CZ rounds off, clouds and scratches. An old ring with pristine edges is a good sign.
- 05
Weigh it if you can
Cubic zirconia is roughly 1.7 times denser than diamond. A CZ that looks the same size as a one carat diamond weighs noticeably more.
Tests that do not work.
- Scratching glass. Moissanite, CZ and quartz all scratch glass. You will damage something for no information.
- The fog test. Diamond clears fast, but so does moissanite. It only rules out obvious glass.
- Water float tests. The density differences are real but the test is unreliable enough to mislead.
- Sandpaper. This ruins stones and settings, and tells you almost nothing.
Certificates, and which ones count.
A grading report from a recognised laboratory is the single biggest factor in what a diamond is worth on resale, because it removes the argument. GIA is the benchmark. AGS and, for some stones, IGI are also recognised.
An appraisal from a retail jeweler is a different document with a different purpose. It is usually written for insurance replacement value, which is not what anyone will pay you for the stone. Do not read one as a price.
If you have the original report, bring it. If you have lost it, the report number is often laser inscribed on the girdle and can be looked up.
Beyond the four Cs.
- Cut quality above all. A poorly cut stone of high colour and clarity still looks dull.
- Whether the stone is natural or lab grown, which the market prices very differently.
- Fluorescence, which can help or hurt depending on the stone.
- The setting, if it is signed by a recognised house.
- Damage, chips and abrasions along the girdle, which are easy to miss and expensive to fix.