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

Amethyst is a purple variety of quartz. Natural and lab-grown amethyst are chemically and physically the same (both are quartz), so many simple tests cannot tell them apart. The challenge is spotting how they formed. This guide shows you how to confirm a stone is amethyst at all, then how to separate natural from lab-grown using practical observations and, when needed, professional tests. You’ll see what to look for, why it matters, and how to avoid damaging your gem.

What “real” means: natural, lab-grown, and imitation

Natural amethyst formed in the Earth. Its internal features record geological growth and stresses. Collectors pay more for natural stones because they are rarer and have provenance.

Lab-grown amethyst is also real quartz with the same chemical composition and hardness. It’s typically made by hydrothermal growth, which mimics natural conditions in a vessel. It costs less and often looks very “perfect” (clean and evenly colored) because growth is controlled.

Imitations are not quartz. Common lookalikes include purple glass, cubic zirconia, synthetic spinel, and plastic. These usually differ in weight, optical properties, and durability.

Tools that help

• 10x loupe or a basic microscope (20–40x is ideal)
• Bright LED flashlight and a white card
• Refractometer and contact liquid (for RI)
• Dichroscope (optional but useful)
• Polariscope or two polarized sunglasses (DIY) for strain/twinning
• Immersion medium (water, baby oil, or glycerin in a clear dish)
• Scale and cup for water displacement (optional SG check)

Step 1: Rule out imitations before you compare natural vs lab-grown

• Look for bubbles. Under 10x, round gas bubbles suspended in a homogenous, featureless interior usually mean glass. Quartz rarely has perfect spherical bubbles. Why this works: glass is melted and often traps gas; quartz grows from solution and forms crystals, not bubbles.
• Check facet wear. Glass scratches and rounds at facet edges quickly. Quartz (hardness 7) keeps crisp, sharp junctions with normal wear. Why: hardness directly affects abrasion resistance.
• Heft test (with care). Cubic zirconia is much heavier than quartz. If two stones are the same size, the CZ will feel noticeably heavier. Why: CZ has a density ~5.8; quartz is ~2.65.
• Conchoidal “orange peel.” Glass often shows an “orange peel” texture on abraded facets under magnification. Quartz does not. Why: glass is amorphous; quartz is crystalline.
• Basic refractive index (RI). Quartz reads ~1.544–1.553 with birefringence ~0.009. Glass imitations usually read lower (~1.50–1.52) and show no birefringence. CZ is much higher (~2.15–2.18). Why: RI is tied to composition and structure and is a reliable screening tool.

Step 2: Confirm the stone is amethyst (purple quartz)

• Color and pleochroism. Amethyst ranges from lilac to deep purple and can show weak to moderate pleochroism—typically purple to reddish-purple—seen with a dichroscope or by rotating the stone over a white card under strong light. Why: anisotropic crystals absorb light differently along crystal directions.
• RI and birefringence match quartz. A reading near 1.544–1.553 and a small double shadow on the refractometer indicate quartz. Why: these are characteristic of trigonal quartz.
• Specific gravity (SG) check. About 2.65 using water displacement. Why: density confirms you’re not dealing with heavier/lighter substitutes.

These tests tell you it’s quartz, but they do not separate natural from lab-grown because both share the same physical constants.

Step 3: Natural vs lab-grown—what to look for under magnification

Hydrothermal growth leaves different “signatures” than geological growth. You are looking for growth patterns, inclusions, and internal strain.

• Color zoning patterns.
  • Natural: Zoning is often uneven and patchy, with irregular bands or clouds. It can concentrate near crystal tips or along faces, rarely forming perfectly straight, repeating lines.
  • Lab-grown: Zoning often forms very regular, straight, or V-shaped chevrons repeating through the stone, sometimes at consistent angles. Boundaries can look crisp and rhythmic.

  Why this works: hydrothermal vessels encourage steady growth along specific faces, creating consistent sectors; natural growth is interrupted by changing temperature, pressure, and chemistry.

• Inclusions and their “behavior.”
  • Natural: Expect “fingerprint” inclusions (healed fractures with tiny fluid-filled trails), multiphase inclusions (liquid plus a gas bubble, sometimes a crystal), wispy veils, and occasional mineral needles or grains. Features are generally irregular and organically arranged.
  • Lab-grown: Often very clean. When present, inclusions tend to align with growth sectors and seed plates. You may see straight, parallel growth lines, sharply bounded zones, or a planar “seed” line crossing the stone. Fluid inclusions are rarer and more orderly.

  Why: natural crystals trap whatever the environment offers and heal over fractures, whereas synthetic growth is engineered to reduce inclusions and grows from a seed plate in stable conditions.

• Strain and twinning under polarized light.
  • Natural: Shows undulatory extinction—wavy light/dark bands moving as you rotate the stone between crossed polarizers. Brazil-law twinning can produce patchy, irregular patterns.
  • Lab-grown: Extinction is more even and uniform, with fewer wavy patches and less evidence of complex twinning.

  Why: geological stresses create internal strain and twinning; controlled growth reduces them.

• Immersion reveals growth architecture. Place the stone in water or baby oil in a clear dish and light it from the side. Zoning and growth lines pop into view.
  • Natural: Irregular, broken, or curved zoning patches.
  • Lab-grown: Repeating, straight, or V-shaped chevrons; sharp sector boundaries.

  Why: immersion reduces surface reflections and lets you see inside more clearly.

Step 4: Clues from color and clarity—useful but not decisive

• Uniform, vivid color + exceptional clarity often suggests lab-grown, because factories can maintain a steady supply of color-causing elements and filter out inclusions. Why: consistent chemistry and fewer impurities during growth.
• Uneven color + natural-looking inclusions often suggests natural origin. Why: fluctuations in natural environments leave a record inside the crystal.

These are trends, not rules. Some natural amethysts are very clean; some synthetics are zoned. Always combine clues.

Practical workflow you can follow

1. Screen out imitations: check for bubbles, facet wear, heft, and RI. If RI is not quartz or you see glass features, stop.
2. Confirm amethyst (quartz): RI ~1.544–1.553, weak pleochroism, SG ~2.65.
3. Immersion and magnification: look for zoning and inclusions. Note patterns: irregular vs chevron/straight; fingerprints vs clean/seedy planes.
4. Polarized light test: look for undulatory extinction (natural) vs uniform extinction (lab-grown).
5. Corroborate with a dichroscope: weak to moderate pleochroism supports amethyst identity but does not determine origin.
6. If the stone is valuable or evidence is mixed: get a professional lab report.

What a professional will do if the stone is important

• Advanced microscopy and immersion: to document growth sectors, twinning, and seed plate features.
• Spectroscopy (UV-Vis, EPR, FTIR) and luminescence: to examine color centers caused by iron and irradiation. Certain spectral features and line shapes differ statistically between natural and hydrothermal quartz.
• Precise polariscopic and strain studies: to characterize twinning and undulatory extinction patterns.

Why these help: the physics of color centers, growth defects, and stress patterns reflect the formation environment and can be measured objectively.

Common pitfalls and how to avoid them

• Don’t do scratch tests. Quartz can scratch glass, but testing can damage a facet and tells you nothing about natural vs lab-grown.
• Don’t rely on color alone. Both natural and lab-grown can be pale or deep. Lighting changes perceived color a lot.
• Beware dyed quartz and glass. Dyed stones can show concentrated color in cracks or near surface-reaching fractures. Look for color concentrations and dye lines under magnification.
• Don’t assume “perfect = fake.” Some natural stones are clean. Use multiple lines of evidence.

Reference values and quick comparison

• Amethyst (natural or lab-grown): RI ~1.544–1.553; birefringence ~0.009; SG ~2.65; hardness 7; weak–moderate pleochroism; often no strong UV fluorescence.
• Purple glass: RI ~1.50–1.52; no birefringence; SG ~2.4–2.6; bubbles; soft edges.
• Cubic zirconia (purple): RI ~2.15–2.18; SG ~5.8; very heavy for size; very high dispersion (“fire”).
• Purple sapphire: RI ~1.76–1.77; SG ~4.0; hardness 9; stronger pleochroism; different inclusion scene.

Real-world examples

• Natural case: 8 mm round with subtle lighter and darker areas under a flashlight. In the loupe: a curved fingerprint near the girdle and a tiny two-phase inclusion (liquid with a movable bubble). Under crossed polars: wavy bands sweeping across the pavilion. Conclusion: natural amethyst.
• Lab-grown case: 10×8 mm oval, vivid uniform purple. Under immersion: crisp, repeating V-shaped chevrons from culet to crown. Almost no inclusions; a straight planar line runs across the stone consistent with a seed plate. Under crossed polars: even extinction. Conclusion: hydrothermal synthetic amethyst.
• Imitation case: 12 mm cushion, bright purple with strong “fire.” Heavy for its size. RI off-scale high. Conclusion: purple cubic zirconia, not quartz.

When to ask for a report

If the stone is large, unusually vivid, or expensive, or if you plan to resell it, a report from a reputable gem laboratory is prudent. The lab can document natural vs lab-grown origin using objective instruments. This protects both buyer and seller and anchors the stone’s value.

Bottom line

First, prove it’s amethyst (quartz) by RI, basic optics, and density. Then, separate natural from lab-grown by how the stone grew: zoning, inclusions, and strain patterns tell the story. Natural stones show irregular, geological “messiness.” Lab-grown stones often show clean interiors with straight or chevron zoning and uniform strain. When the clues disagree—or the stakes are high—get a lab to confirm. That workflow is accurate, safe for your gem, and repeatable.