Natural vs. Lab-Grown Gems: The Ultimate Buyer’s Guide, How to Tell If Your Jeweler Is Selling You a Synthetic Stone.

Natural or lab-grown? For gems, the differences are real—but not always where you think. This guide explains how each type is made, how they look and behave, how pricing works, and the specific checks that help you avoid paying natural-stone prices for a synthetic. You’ll get plain, practical steps you can use at the counter and at home, plus the paperwork that protects you.

What “natural,” “lab-grown,” and “simulant” really mean

Natural gems form in the earth over millions of years. They carry trace elements, growth marks, and inclusions that reflect geology and mining.

Lab-grown gems have the same chemical composition and crystal structure as their natural counterparts but are grown in factories. A lab-grown diamond is a real diamond; it just formed in weeks, not eons.

Simulants look like a gem but are different materials. Cubic zirconia (CZ) and moissanite are diamond simulants. They mimic look and sparkle but differ in properties, price, and durability. This matters because testers and prices behave very differently with simulants.

How lab-grown gems are made and why it matters

Growth method leaves fingerprints you can detect.

• Diamonds: HPHT (high pressure, high temperature) grows crystals in a press; CVD (chemical vapor deposition) grows them layer by layer in a chamber. HPHT can trap metallic flux inclusions and shows specific phosphorescence patterns. CVD often shows flat growth layers and may need post-growth treatment to improve color. These artifacts help experts identify origin.
• Ruby and sapphire (corundum): Flame-fusion (Verneuil) is fast and cheap; it often leaves curved growth lines and round gas bubbles. Flux and hydrothermal methods create more natural-looking inclusions but still show tell-tale features like flux residue or chevron growth.
• Emerald: Hydrothermal growth uses high-temperature solutions. Synthetic emeralds may show “nail-head spicules,” chevron zoning, and ultra-clean, unnatural clarity. Many natural emeralds are oil- or resin-filled to mask fractures; that treatment leaves its own clues.
• Opal: Synthetic opal often shows a tidy, repeating “lizard-skin” or “chicken-wire” pattern in the play-of-color. Natural opal is more random and may show potch (common opal) layers.

Why it matters: growth clues plus lab reports let you separate natural, lab-grown, and simulants. Without that, prices and value can be wildly off.

Reliable ways to tell natural from lab-grown

There is no single consumer test that is always conclusive. Use a stack of evidence.

• Start with paperwork: A graded report from a trusted lab (for example, major gemological labs widely used in the trade) should clearly say “laboratory-grown,” “lab-created,” or the specific treatment. Reports list measurements, grade, and often a laser inscription number you can match on the girdle with a loupe. Why it works: documentation travels with the stone and is hard to fake convincingly across all data points.
• Magnification (10× loupe): Look for diagnostic inclusions and growth features.
  • Curved growth lines or perfectly round bubbles in ruby/sapphire suggest flame-fusion synthetic.
  • Flux residue in ruby/sapphire/emerald (wispy, reflective “fingerprints”) can indicate synthetic growth in flux.
  • HPHT diamond may show metallic specks; CVD can show flat growth striations.
  • Glass-filled rubies show a “blue flash” in healed fractures and gas bubbles trapped in glass.

  Why it works: nature rarely makes perfectly regular curves or spotless interiors in colored stones; growth labs leave characteristic debris or zoning.

• UV reaction and phosphorescence: Lab instruments read fluorescence/phosphorescence patterns that differ by growth method. At the counter, a jeweler’s UV lamp can show clues, but patterns overlap. Use as supporting evidence, not proof.
• Conductivity testers (diamonds): Thermal diamond testers can be fooled by moissanite. A combined thermal/electrical tester separates diamond from moissanite. Why it works: diamond and moissanite handle heat and electricity differently. Note: this does not separate natural from lab-grown diamond.
• Birefringence/doubling (moissanite): Through the pavilion, you may see doubled facet edges in moissanite due to birefringence. Hard to see in small or well-cut stones. Useful to rule out a simulant, not lab vs natural diamond.
• Weight and optics (simulants): CZ is much heavier than diamond for the same size and has “softer” sparkle. Good bench jewelers notice instantly. Again, this flags simulants, not lab-grown.
• Independent confirmation: For high-value buys, an independent gemologist with advanced instruments (spectroscopy, microscopy, polariscope) can make a definitive call. Why it works: lab-grown often reveals itself under polarized light, spectroscopy, or photoluminescence that consumers can’t access.

Stone-by-stone tips you can use

• Diamond
  • Check for a laser inscription that matches a grading report. Many lab-grown diamonds are inscribed as such.
  • Use a combined diamond/moissanite tester first. If it reads diamond, you still need a report to know natural vs lab-grown.
  • Under a loupe, metallic flecks can hint HPHT; layered growth can hint CVD. These are clues, not final proof.
  • Beware “too perfect” large diamonds at surprising prices with no lab report.
• Ruby & Sapphire
  • Curved color bands or growth lines = likely flame-fusion synthetic.
  • Color concentrated at facet junctions can indicate surface diffusion treatment.
  • Look for natural inclusions: rutile needles (silk) arranged in straight patterns are common in naturals; melted or re-healed silk may indicate heat treatment. Ask for disclosure in writing.
• Emerald
  • Natural emeralds usually have a “jardin” (garden) of inclusions. Ultra-clean emeralds at low prices are suspect.
  • Hydrothermal synthetics can show chevron zoning and nail-head spicules.
  • Fracture filling (oil/resin) shows an orange/blue “flash effect” under a fiber-optic light. That is a treatment, not origin, and must be disclosed with degree of filling.
• Opal
  • Synthetics often show a neat, repeating “lizard-skin” color patchwork. Natural play-of-color is more irregular.
  • Check the side: doublets/triplets show a distinct layered structure with glue lines and a dark backing.
• Alexandrite
  • Lab-grown often has a very strong, clean color change and neat growth features. Naturals show more mixed inclusions and subtler hues. Confirm with a report on anything valuable.

Price, resale, and value

• Lab-grown diamonds: Typically 70–85% less than natural diamonds of the same size and grade. Supply is scalable, so resale is low. Expect steep depreciation.
• Lab-grown colored stones: Often 80–95% less than fine natural equivalents. Great looks for little money, but resale is minimal.
• Natural gems: Scarcity supports value. Still, retail-to-resale gaps are large; expect 20–50% of retail in secondary markets, depending on quality and documentation.

Why this matters: price outliers and “too perfect” stones with no paperwork are risk flags for undisclosed synthetics or treatments.

Ethics and environmental claims—read them critically

Mining can harm communities and ecosystems; well-managed mines can support livelihoods. Lab production avoids digging but uses energy; impacts vary with the power source. Marketing claims often cherry-pick data. Ask for specifics: energy mix, mine origin, third-party audits, and whether the metal is recycled. Traceability and clear disclosure beat broad slogans.

Paperwork that protects you

• Grading report: For diamonds and valuable colored stones, ask for a report from a recognized lab. The report should state natural vs laboratory-grown and list treatments. Match the laser inscription to the report number when possible.
• Written sales receipt: The description must include “laboratory-grown” or “lab-created” where applicable and disclose treatments (heat, diffusion, fracture-filling, HPHT, etc.). Verbal claims are not enough.
• Appraisal: For insurance, get an appraisal that copies the lab details and inscription number. This helps prevent stone-swaps and simplifies claims.

How to shop: questions to ask your jeweler

• Is this stone natural, laboratory-grown, or a simulant? Please write that on the receipt.
• What treatments has it received? To what degree? Is the treatment stable (heat, diffusion, filling)?
• Do you have a grading report? Can we inspect the laser inscription under a loupe?
• What is your return policy, and do you offer a buyback or upgrade program?
• Will you allow an independent appraisal before the sale is final?

Red flags your jeweler may be selling synthetics as natural

• Unusually low price for high color/clarity without a lab report.
• Reluctance to put “lab-grown” or treatments in writing.
• No return period and pressure to “buy today.”
• Vague claims like “same as natural” without saying “lab-grown.”
• Refusal to let you verify a laser inscription or to measure the stone.

At-home checks you can try (with caution)

• Loupe check: Look for curved growth lines (synthetic flame-fusion corundum) and obvious bubbles in colored stones. Not definitive, but useful.
• Testers: A combined diamond/moissanite tester can weed out simulants quickly. It cannot separate natural vs lab-grown diamond.
• Avoid myths: Scratch tests, fog tests, and “read-through” tests are unreliable and can damage the gem. Do not use them.

If you suspect misrepresentation

• Pause the purchase. Ask for everything in writing.
• Get an independent gemologist’s opinion. If the stone is mounted, ask about testing limitations and fees for unsetting.
• If you already bought it, use the return policy. If denied, your credit card issuer may help if you have documentation.
• For significant disputes, a formal lab report is the strongest evidence.

Bottom line

Lab-grown gems are real gemstones with real beauty. Natural gems carry rarity and history. The right choice depends on your budget and values. What you must not do is pay natural-stone prices for a synthetic. Protect yourself with a grading report, written disclosures, a quick loupe check, and a fair return policy. When in doubt, bring in an independent expert. Clear evidence—not sales talk—should drive your decision.