How to identify real Diamonds vs lab-grown ones: Expert identification guide

Natural and lab-grown diamonds are both real diamonds. They share the same chemical formula and most physical traits. That makes them hard to tell apart. If you want to know what you’re buying, you need a methodical approach. This guide explains what you can check at home, what trained gemologists look for under magnification, and when a lab report is the only safe answer.

Real, lab-grown, and simulants: what you’re actually comparing

• Natural diamond: Carbon crystal formed in the earth over millions of years. Often contains natural inclusions and irregular growth patterns.
• Lab‑grown diamond (HPHT or CVD): Same carbon crystal, grown in a factory. HPHT uses high pressure and temperature; CVD grows diamond layer by layer in a vacuum. Growth method leaves tell‑tale features.
• Simulants (not diamond): Materials that look like diamond but aren’t. Common ones are moissanite and cubic zirconia (CZ). These can be separated quickly with simple tools.

Why this matters: tests that separate diamond vs non‑diamond (like a thermal tester) will not separate natural vs lab‑grown. You need different clues for each question.

Quick, safe checks you can do at home

• Look for a laser inscription on the girdle. Many lab‑grown diamonds are inscribed “LAB GROWN,” “LG,” or similar. Use a 10× loupe and good light. Why it helps: disclosure is common and easy to read if present. Limit: not all stones are inscribed, and inscriptions can be worn or removed.
• Use a moissanite tester. If you’re unsure whether the stone is diamond or moissanite, this tool pays for itself. Why: moissanite conducts electricity differently from diamond. Thermal testers alone often misread moissanite as diamond; a combo thermal/electrical tester is best.
• Check under a 10× loupe. Clean the stone. Look for:
  • Natural diamond clues: mixed, irregular inclusions such as tiny crystals, feathers, needles, and wispy twinning patterns.
  • HPHT clues: pinpoint or plate‑like metallic inclusions; geometric growth zoning; occasionally a faint magnetic response due to metallic flux (weak magnetism is rare but meaningful).
  • CVD clues: fine, parallel growth lines or bands (“striations”) and tiny dark pinpoints in streaks; uneven color zoning layer by layer.

  Why: growth environment leaves characteristic “fingerprints.” Limit: clean stones may show few visible inclusions.

• Longwave UV flashlight (365–395 nm). In a dark room:
  • Observe fluorescence color and pattern. Natural stones often show even blue (or none). CVD stones can show uneven, banded fluorescence following growth lines. HPHT stones may show blue fluorescence and sometimes a brief afterglow.
  • Note any phosphorescence (afterglow once the light is off). Some HPHT stones show a visible blue afterglow; some CVD show orange‑red. Not all do.

  Why: defects in the crystal (created by different growth methods) respond differently to UV. Limit: overlap exists; UV alone is not conclusive.

• Facet doubling test (for simulants). Through the pavilion, look at a back facet line. If you see a doubled edge that shifts as you tilt, suspect moissanite (birefringent). Diamond is singly refractive and shows clean, single lines. Limit: this is easier with loose stones and some moissanite cuts mask doubling.

What professionals examine under magnification

Gemologists combine several observations because no single clue is perfect.

• Inclusion type and distribution.
  • Natural: mineral crystals (garnet, olivine), feathers, clouds, knots, and irregular “twinning wisps.” These look organic and uneven.
  • HPHT: metallic flux inclusions (tiny reflective platelets/needles), blocky zoning by growth sectors, sometimes etch channels.
  • CVD: parallel growth striations, pinpoint clouds in layers, occasional plate‑like graphitic inclusions.

  Why: different factories and the earth create different internal “landscapes.”

• Graining and growth morphology. Natural stones show complex, intersecting graining and octahedral growth features. HPHT often shows sector zoning from cuboctahedral growth. CVD shows flat, layered growth; lines often run in one direction. Why: crystal grows along different faces in each method.
• Strain patterns under crossed polars. With a polariscope (or two polarized lenses), natural diamonds often display irregular cross‑hatched or “tatami” patterns. CVD tends to show straight, banded patterns; HPHT can show sectorial patterns. Why: internal strain locks in differently based on growth and treatment.
• Fluorescence mapping and phosphorescence. Labs compare longwave vs shortwave UV, color, intensity, and afterglow duration. Banding that matches growth layers points to CVD. Persistent blue afterglow can suggest HPHT. Why: defects like nitrogen‑vacancy or boron centers respond in known ways.
• Spectroscopy and type classification. FTIR, photoluminescence, and cathodoluminescence reveal impurity “signatures.” Many colorless CVD diamonds are Type IIa with characteristic peaks; HPHT may show features related to metallic catalysts or boron; naturals show different nitrogen aggregates. Why: impurities are the most reliable lab markers.

Separating diamond from simulants (fast and reliable)

• Moissanite: High brilliance and fire, often shows doubled facet edges. Conducts heat like diamond, so thermal testers fail. Use a moissanite tester (electrical) or check for birefringence with a loupe. Why: moissanite’s crystal structure is different.
• Cubic zirconia (CZ): Heavier for the same size, lower hardness, “glassy” look, and usually no UV fluorescence. Thermal testers quickly flag CZ as non‑diamond. Why: CZ conducts heat poorly compared with diamond.
• White sapphire, glass: Lower brilliance and hardness; glass often shows bubbles. Thermal testers also separate these from diamond.

Key point: first confirm you truly have diamond (natural or lab‑grown). Then evaluate origin.

Myths to ignore (and why they mislead)

• “Scratch test” on glass. Diamond can scratch glass, but so can moissanite and other materials. You can also chip your stone. It proves nothing and risks damage.
• “Fog test.” Breathing on the stone to see how fast it clears is unreliable. Oils, dirt, and room conditions affect results. Both natural and lab‑grown diamond clear quickly.
• “Newspaper/read‑through” test. Well‑cut diamonds scatter light; many settings block the pavilion. You can’t depend on this, and moissanite can behave similarly.
• Color or “too perfect” clarity means lab‑grown. Some natural diamonds are very clean; some lab‑grown stones have visible inclusions. Visual perfection is not a diagnosis.

When to insist on a lab report

• Any significant purchase. Ask for a grading report from a recognized lab that explicitly states “Laboratory‑Grown” or “Natural.” The report number often matches an inscription on the girdle.
• If the seller cannot disclose origin in writing. Walk away or plan to submit the stone to a lab.
• If your own checks conflict. Mixed signals (e.g., banded fluorescence but natural‑looking inclusions) call for lab spectroscopy.

Why this matters: pricing, insurance, and resale all depend on correct disclosure. A report also records treatments (e.g., post‑growth HPHT or irradiation).

HPHT vs CVD: practical tells and caveats

• HPHT clues: occasional metallic flux inclusions (can cause weak magnetism), sector zoning, strong blue fluorescence with possible brief blue afterglow. Some stones show “cross‑like” fluorescence patterns tied to growth sectors.
• CVD clues: parallel growth striations, layered color/graining, uneven or banded fluorescence that follows those layers; in some cases, orange‑red fluorescence or afterglow from certain defects.
• Caveat: post‑growth treatments can reduce or mask these features. That’s why labs rely on spectroscopy, not a single visual clue.

An actionable workflow you can follow

1. Confirm it’s diamond. Use a combo thermal/electrical tester to rule out CZ and moissanite. If it’s not diamond, you’re done.
2. Check for girdle inscription. Use a 10× loupe. Record any letters/numbers. “LAB GROWN” or equivalent answers the question.
3. Loupe for inclusions and growth features. Note anything metallic, banded, or layered (lab‑grown clues) versus mixed, irregular naturals.
4. UV flashlight test in the dark. Observe color, intensity, evenness, and afterglow. Photograph what you see for reference.
5. Optional polarization check. If you have two polarized lenses, look for banded vs irregular strain patterns.
6. If any doubt remains, get a lab report. For mounted stones, request verification without unsetting if possible, or be prepared to unset for full analysis.

Buying tips to avoid surprises

• Ask origin upfront and get it in writing. “Natural” and “Laboratory‑Grown” are standard terms. Avoid vague language like “real diamond” without origin.
• Match the report to the stone. Verify the report number inscribed on the girdle and that color, clarity, and measurements align.
• Mind pricing. Lab‑grown diamonds usually cost less for the same size/grade. A “too‑good” price for a supposed natural diamond is a red flag.
• Know the return and upgrade policy. Policies sometimes differ for lab‑grown vs natural. Get details before you buy.

The bottom line: separating diamond from simulants is easy with a good tester. Separating natural from lab‑grown takes careful observation and often lab tools. Use inscriptions, a loupe, and UV as screening steps, but rely on a reputable lab report when the answer matters. That way you get what you paid for—and you can prove it later.