How to identify real Garnets (Demantoid/Tsavorite) vs lab-grown ones: Expert identification guide

Bright green garnets can be confusing. Demantoid and tsavorite are both natural green garnets, but many “lab-grown garnets” on the market are different man‑made materials (like YAG or GGG) or other simulants sold under vague names. This guide shows you how to separate real demantoid and tsavorite from lab-grown and look‑alike stones using practical, evidence‑based checks. You’ll see what to look for, why it works, and when to get a lab report.

What “real” vs “lab-grown” means in green garnets

Real (natural) green garnets in jewelry are usually:

• Demantoid (variety of andradite). Known for very high fire (dispersion) and often a slightly yellowish green. RI ~1.88, SG ~3.84.
• Tsavorite (green grossular). A vivid, pure to slightly yellowish green. RI ~1.74–1.76, SG ~3.60–3.68.

“Lab-grown garnet” in trade is usually not synthetic demantoid or tsavorite. It’s typically other synthetic garnet-structure materials made for industry and jewelry:

• YAG (yttrium aluminum garnet): RI ~1.83, SG ~4.5–4.6.
• GGG (gadolinium gallium garnet): RI ~1.97, SG ~7.0+.

These can be cut green and sold as “lab garnet,” but they are not the same species as natural demantoid or tsavorite. There are also common simulants (CZ, glass, synthetic spinel, synthetic sapphire, moissanite).

Fast visual cues before you reach for tools

• Fire (rainbow flashes): Demantoid shows conspicuous fire even in dim light because it has very high dispersion. Tsavorite’s fire is modest. If flashes look stronger than diamond, consider CZ or moissanite; if unusually low for a “demantoid,” suspect YAG or glass.
• Color character:
  • Demantoid: often slightly yellowish green; can look “sparkly” because fire competes with body color.
  • Tsavorite: a pure, saturated green (often compared to emerald) with less rainbow flash than demantoid.
  • YAG/GGG: color often very uniform and “neon” or “flat.”
  • Glass: tends to be an even, simple green with little life.
• Facet edges and surface wear: Glass dulls and abrades quickly. CZ keeps razor‑sharp edges. Natural garnets hold edges well but can show minor wear on old jewelry.
• Doubling seen with a loupe: Garnets are singly refractive. If you see obvious double facet-edge images, think moissanite or other doubly refractive stones, not garnet.

Inclusions that speak volumes

Inclusions are often the fastest, most reliable separator—if you know what to look for.

• Demantoid “horsetails”: Radiating, golden to greenish fibrous inclusions that sweep out from a dark crystal (often chromite). These are diagnostic for natural demantoid. Not every demantoid shows them, but when present they confirm a natural demantoid beyond doubt.
• Other demantoid signs: Tiny crystals, scattered needles, and “strain” under crossed polars are normal. Extremely clean demantoid exists, but is less common.
• Tsavorite clues: Typical natural features include small crystals (diopside, apatite), wispy “fingerprint” healing patterns, and fine needles or feathers. A few pinpoint “sugar” granules may appear. These patterns vary by source but look organic rather than “engineered.”
• YAG/GGG: Often very clean. If present, you may see neat, straight growth striae or faint banding; in flux-grown synthetics, wispy “flux veils” or metallic-looking platelets can occur.
• Glass: Round bubbles (perfect spheres), swirl marks, and flow lines are common. These are rarely seen in natural garnets.
• CZ: Usually very clean; may show subtle internal “swirl” or tiny opaque platelets. Edges are exceptionally crisp.

Why it works: Natural crystals grow under changing geological conditions, so inclusions are irregular and varied. Man‑made materials grow under tightly controlled conditions, producing cleaner stones with repetitive or telltale growth features.

At‑home checks that actually help

• Heft test: GGG and CZ feel unusually heavy for their size; glass feels light. This is crude, but extremes are obvious.
• Simple water displacement SG: If unmounted, weigh the stone in air and then in water to estimate specific gravity.
  • Demantoid: ~3.8–3.9
  • Tsavorite: ~3.6–3.7
  • YAG: ~4.5–4.6 (heavy)
  • GGG: ~7+ (very heavy)
  • CZ: ~5.8
  • Glass: ~2.5

  A reading far from garnet ranges signals a lab material or simulant.

• UV lamp: Most natural green garnets are inert to weak under longwave and shortwave UV. Strong fluorescence suggests a simulant, but many synthetics are also inert—so treat this as a supporting clue only.
• Avoid scratch tests: They damage stones and don’t cleanly separate garnet from many look‑alikes.

Gemological instruments: the decisive toolkit

If you can access basic instruments, these tests separate species quickly.

• Refractometer (spot method for mounted stones):
  • Demantoid (andradite): RI ~1.88 (single shadow edge; isotropic).
  • Tsavorite (grossular): RI ~1.74–1.76 (isotropic).
  • YAG: ~1.83.
  • GGG: ~1.97.
  • CZ: ~2.15 (very high).

  Why it works: RI is a fundamental optical property tied to composition. Lab-grown YAG/GGG cannot “fake” the RI of natural demantoid or tsavorite.

• Polariscope:
  • Garnets are isotropic (stay dark when rotated), but many show faint anomalous double refraction due to strain.
  • Moissanite and many other simulants are clearly double refractive.
• Spectroscope:
  • Tsavorite: an emerald‑like spectrum with chromium/vanadium absorptions—few, distinct bands that make the red region partially absorbed and the green transmit strongly.
  • Demantoid: chromium/iron features; Russian stones with more chromium may show clearer bands. Overall pattern is less “lined” than rare‑earth‑doped synthetics.
  • YAG/GGG or glass doped with rare earths: multiple sharp, evenly spaced lines (rare‑earth signature) across the yellow‑red region. This “barcode” look is a red flag for synthetics or treated glass.

  Why it works: Different coloring ions absorb light in unique ways. Chromium/vanadium patterns differ from rare‑earth dopants used in many synthetics.

• Observing dispersion (“fire”):
  • Demantoid: very high fire that competes with body color.
  • Tsavorite: more restrained fire.
  • CZ and moissanite: extremely high fire; moissanite also shows doubled facet edges.
• Hydrostatic SG: Confirms or challenges your RI result. YAG and especially GGG read much heavier than natural garnets.

Demantoid vs. tsavorite: don’t mix the naturals

• Color: Demantoid leans yellow‑green; tsavorite is a purer emerald‑like green.
• Fire: Demantoid is fiery; tsavorite is calmer.
• RI/SG: Demantoid ~1.88/~3.84; tsavorite ~1.74–1.76/~3.6–3.7.
• Inclusions: Horsetails confirm demantoid. Tsavorite lacks horsetails but can show natural crystal inclusions and fingerprints.

Why it matters: You must know which natural species you have before deciding if it matches the properties of a lab-grown look‑alike.

Common traps and how to avoid them

• “Lab-grown demantoid/tsavorite” claims: True synthetics of these exact species are not common in the market. Verify with RI and SG—YAG/GGG will betray themselves.
• Coatings and surface films: Some stones are color‑coated. Look for concentrated color on the girdle or pavilion facet junctions; magnification shows patchy films or wear-through.
• Assembled stones: Doublets/triplets can combine green glass with clear crowns or pavilions. Inspect the girdle for a seam.
• Heat treatment: Mild heating of demantoid to improve color exists but is hard to detect without a lab. Tsavorite is generally not treated; claims of “heated tsavorite” should raise questions.
• Mislabeling as “emerald”: Tsavorite’s color invites this. RI and SG cleanly separate tsavorite from emerald.

Step‑by‑step identification workflow

• 1) Loupe at 10×: Look for horsetails (demantoid), natural crystal inclusions/fingerprints (tsavorite), or telltale synthetic features (bubbles, flux veils, rare-earth “cleanliness”). Note facet wear and any coating at the girdle.
• 2) Observe fire and color: Strong, lively rainbow flash suggests demantoid; subdued fire suggests tsavorite; “too much” fire or doubling suggests CZ/moissanite.
• 3) Refractometer: Record RI. Around 1.88 = demantoid range; 1.74–1.76 = tsavorite. ~1.83 = YAG; ~1.97 = GGG; ~2.15 = CZ.
• 4) Spectroscope: Look for chromium/vanadium bands (natural greens) versus multiple sharp rare‑earth lines (synthetics/glass).
• 5) Hydrostatic SG: Confirm: 3.6–3.9 = natural garnet ranges; 4.5–7+ = synthetic garnet (YAG/GGG) territory.
• 6) Polariscope (optional): Isotropic response supports garnet; obvious DR points away from garnet.
• 7) Conclusion: Properties either cluster around demantoid or tsavorite, or they don’t. Any mismatch (e.g., RI 1.83 with perfect cleanliness) points to YAG or another simulant.

When only a lab can settle it

• High-value stones or those lacking clear inclusion clues.
• Origin questions (e.g., “Russian demantoid”) that affect price.
• Treatment detection (heat, coatings, any filling).

Ask for a report that clearly states species (andradite or grossular), variety (demantoid or tsavorite), natural vs synthetic, and any treatments. For expensive purchases, have the seller put “natural demantoid/tsavorite, no treatments disclosed” on the invoice.

Quick red flags checklist

• Very heavy feel for size, or SG above 4.0 → suspect YAG, GGG, or CZ.
• RI around 1.83 or ~1.97 → synthetic garnet varieties, not demantoid/tsavorite.
• Round bubbles/flow lines → glass.
• Extreme fire with doubled edges → moissanite.
• Perfectly clean “neon” green with mismatched RI/SG → likely synthetic.
• Horsetail inclusions → natural demantoid confirmed.

The bottom line: identify the species first with RI and SG, then confirm with inclusions and optical behavior. Demantoid and tsavorite each occupy a tight, well-known property range. Lab-grown “garnets” (YAG, GGG) and other simulants fall outside those ranges and reveal themselves quickly if you measure the right things.