Free Diamond Identifier by Photo —
Real Diamond or Simulant?

How to Identify a Diamond — What the AI Looks For

When you upload a photo to our free diamond identifier, the AI analyses the same visual properties a gemologist would examine during an initial screening. Understanding these properties helps you take better photos and interpret your results more confidently.

Brilliance vs Fire

Brilliance is the white light reflected back from a stone — the sparkle you see in normal lighting. Fire (dispersion) is the rainbow-coloured flashes when light splits through the stone. Diamond shows strong brilliance with moderate fire. Cubic zirconia typically shows excessive fire — more rainbow flashes than a comparable diamond. Moissanite also shows stronger fire than diamond. If your stone produces dramatic rainbow flashes in ordinary room light, it may be a simulant rather than diamond.

Facet Edge Sharpness

Genuine diamond is cut with extremely sharp facet junctions where each flat face meets the next. Under magnification or in a good macro photo, these lines appear crisp and precise. Cubic zirconia and glass simulants often show slightly rounded or soft facet edges — a subtle but reliable clue visible in side-lit macro photos. This is one of the most useful visual screening tests available from photographs.

Cut Symmetry and Proportions

Well-cut diamonds show balanced symmetry — facets mirror evenly across the stone, the table is centred, and the girdle is uniform. Poor symmetry or off-centre tables can indicate lower-quality cutting or simulants cut to maximise carat weight rather than optical performance. Our AI assesses overall cut quality and symmetry when visible in your photos.

Double Refraction (Moissanite Clue)

Diamond is singly refractive — light passes through without splitting. Moissanite is doubly refractive, meaning facet lines can appear doubled when viewed through the table under magnification. This “facet doubling” is one of the most reliable ways to distinguish moissanite from diamond, though it requires magnification to see clearly. Mention in your notes if you observe doubled facet lines.

Hardness and the Scratch Test

Diamond is the hardest natural material on Earth — Mohs 10. It scratches all other gemstones and glass easily. Cubic zirconia (Mohs 8–8.5), moissanite (Mohs 9.25), white sapphire (Mohs 9), and glass (Mohs 5–6) are all softer. Warning: never scratch a stone you do not own, and be aware that scratching a simulant with diamond dust on a testing plate can damage it. Mention scratch test results in your notes rather than performing destructive tests on valuable pieces.

Diamond vs Common Simulants — Quick Comparison

These are the stones most frequently confused with diamond. Understanding their key differences helps you interpret your screening result.

Diamond vs Cubic Zirconia (CZ)

CZ is the most common diamond simulant worldwide. Key differences: CZ shows heavier rainbow fire than diamond; facet edges are slightly rounded; CZ is flawless (no natural inclusions); CZ is softer (Mohs 8–8.5 vs diamond Mohs 10); CZ is significantly denser and feels heavier for its size. CZ costs pennies per carat; even a small natural diamond costs hundreds. If you paid very little for a “diamond,” CZ is the most likely explanation.

Diamond vs Moissanite

Moissanite is increasingly popular as a diamond alternative in engagement rings. Key differences: moissanite shows stronger fire (more rainbow flashes); moissanite shows double refraction (doubled facet lines under magnification); moissanite is slightly softer (Mohs 9.25); moissanite has higher thermal conductivity similar to diamond. Moissanite is a legitimate gemstone in its own right — the question is whether you were sold moissanite as diamond.

Diamond vs White Sapphire

White sapphire is a natural corundum used as a budget diamond alternative. Key differences: white sapphire shows lower brilliance and fire; often appears slightly milky or hazy; may contain natural inclusions; Mohs 9 (hard but not as hard as diamond); significantly less expensive. White sapphire does not produce the sharp, bright sparkle of a well-cut diamond.

Diamond vs Glass

Glass and rhinestone simulants appear in costume jewellery and vintage pieces. Key differences: very soft (Mohs 5–6); rounded facet edges; visible bubbles or mould marks under magnification; dull sparkle compared to diamond; often set in base metal rather than gold or platinum. If your stone is in a cheap setting with no metal stamp, glass is a strong possibility.

Simple Home Tests for Diamond Screening

While our AI works from photos alone, these quick tests help you provide better context in the notes field. None of these are definitive on their own.

The Fog Test

Breathe on the stone like fogging a mirror. Diamond disperses heat rapidly — the fog clears in 1–2 seconds. Simulants like CZ and glass hold the fog longer (3–5 seconds or more). Moissanite also clears quickly, so this test alone cannot distinguish diamond from moissanite. Clean the stone first for accurate results.

The Water Drop Test

Place a drop of water on the table of a loose stone. On diamond, the water bead maintains a tight, high dome due to diamond’s high surface tension. On glass and some simulants, the water spreads more flatly. This is a rough indicator only — not definitive.

The Read-Through Test

Place the stone table-down on a line of printed text. With a genuine round brilliant diamond, you typically cannot read the text through the stone due to total internal reflection. With CZ and some simulants, the text may be readable through the pavilion. Results vary with cut quality and stone size.

The UV Light Test

Approximately 30–35% of natural diamonds fluoresce blue under long-wave UV light. This is not definitive — many diamonds do not fluoresce, and some simulants also fluoresce. Lab-grown diamonds may show different fluorescence patterns. Mention any UV response in your notes.

Natural Diamond vs Lab-Grown Diamond

Lab-grown (synthetic) diamonds are chemically and optically identical to natural diamonds — both are pure carbon with Mohs 10 hardness. They cannot be distinguished by appearance, hardness, or basic home tests. The only reliable methods require specialised laboratory equipment:

• Photoluminescence spectroscopy — detects growth patterns unique to lab creation methods (HPHT or CVD)
• Microscopic examination — reveals metallic flux inclusions (HPHT) or strain patterns (CVD) not found in natural diamonds
• Isotope analysis — carbon isotope ratios differ between natural and lab-grown stones
• GIA or IGI report — explicitly states natural or laboratory-grown origin

Our AI will note when a stone appears consistent with diamond but cannot confirm natural vs lab-grown origin from photos alone. Always request a lab report when origin matters for value or disclosure.

Understanding the 4Cs

The GIA 4Cs — Cut, Colour, Clarity, and Carat — are the international standard for grading diamonds. Our AI provides educational context but cannot assign official grades from photos alone:

• Cut — how well the stone’s proportions maximise light return. Our AI can assess visible symmetry and proportions from good photos.
• Colour — graded D (colourless) to Z (light yellow/brown). Photo colour is affected by lighting and white balance; accurate grading requires controlled conditions.
• Clarity — internal inclusions and external blemishes graded FL to I3. Macro photos can reveal visible inclusions but cannot match loupe grading at 10× magnification.
• Carat — weight (1 carat = 0.2 grams). Provide weight in your notes if known; our AI cannot weigh stones from photos.

When to Get a Professional Appraisal

Always consult a certified gemologist or get a GIA/IGI/AGS lab report when:

• You are buying or selling a diamond and need to confirm authenticity and value
• You need insurance documentation for a valuable piece
• You were told a stone is diamond but suspect it may be a simulant
• You need to know whether a diamond is natural or lab-grown for disclosure purposes
• The stone is set in an antique or estate piece with unknown provenance
• You need official 4Cs grading for a significant purchase or sale

Using Our Specialist Identifier Tools

Our diamond identifier focuses specifically on diamond vs simulant screening. For other gemstones, use our specialist tools: gemstone identifier for faceted gems and jewellery, sapphire identifier for blue stones, ruby identifier for red stones, and crystal identifier for rough crystals and mineral specimens. For gold jewellery settings, our gold identifier helps screen gold content separately.