1. The price it came at
Diamond pricing is brutally consistent because the trade runs on published per-carat price sheets. A one carat stone of decent colour and clarity has a floor, and that floor is a long way above what most suspicious stones cost. If the price feels like a stroke of luck, the explanation is usually the stone rather than the seller's generosity.
2. What it is set in
This is the fastest read in the whole list. Look inside the band for a stamp: 375, 585, 750 for gold, 925 for sterling silver, PT or 950 for platinum. An unmarked band, or one where the plating has worn through to a grey base metal, tells you what the maker thought the stone was worth.
Sterling silver in particular is a flag on anything claiming to be a significant diamond. It is too soft to secure a valuable stone and no jeweller would use it for one.
3. Whether there is paperwork
Anything meaningful should arrive with a grading report from an independent laboratory. GIA is the strictest and most widely trusted. IGI is common, especially on lab-grown stones. A till receipt is not a report, and a certificate from a lab with no findable web presence is worth exactly nothing.
4. How it throws light
Diamond returns mostly white brilliance with disciplined flashes of colour. Simulants disperse light more strongly, so they scatter more rainbow. It is a soft signal because a badly cut diamond looks dull and a well cut CZ looks spectacular, but combined with anything else on this list it adds up.
| Stone | Dispersion | What you see |
|---|---|---|
| Diamond | 0.044 | White brilliance, controlled fire |
| Cubic zirconia | 0.060 | Noticeably more rainbow |
| Moissanite | 0.104 | Very high fire, almost oily flashes |
| Glass | Low | Flat, lifeless |
5. Whether it is too clean
A loupe costs about ten dollars and this is what it is for. Natural diamonds nearly always carry inclusions. A completely clean stone at a modest price is a warning sign, not a windfall. While you are looking, check whether the facet edges appear doubled, which points straight at moissanite.
6. The condition of the edges
Diamond is a 10 on the Mohs scale and everyday life does not mark it. Cubic zirconia is an 8 to 8.5 and after a year or two of being worn it picks up scuffing on the facet edges and around the girdle, and can go slightly cloudy. An old stone with soft, rounded edges is telling you something.
7. What the seller will let you do
Any legitimate seller will let you take a stone to an independent jeweller before money changes hands. Reluctance, urgency, or a discount that expires if you leave the shop are the oldest signals in the business and they have not stopped working.
Not sure what you are looking at?
Photograph the stone and the app gives you a visual read on the 4Cs, an estimated value range, and what to check next. Free on iOS and Android.
Frequently asked questions
What is the single biggest giveaway?
Does too much sparkle mean it is fake?
Should a real diamond be flawless?
What paperwork should come with a real stone?
Worth being clear: everything here, and the app itself, is an educational reference. At-home tests narrow things down, they do not certify a stone. Before you buy, sell or insure anything of real value, get it looked at by a certified gemologist or an independent appraiser.