Synthetic Gemstones
Synthetic gem production methods including flame fusion, hydrothermal, flux growth, and detection techniques.
Introduction
A synthetic gemstone shares the same chemical composition, crystal structure, and
physical properties as its natural counterpart, grown in a laboratory rather than
the Earth. This distinguishes synthetics from simulants, which merely resemble
another gem without matching its composition. Four growth methods are commercially
significant: flame fusion (Verneuil, 1902) produces synthetic ruby and sapphire
characterised by diagnostic curved striae and spherical gas bubbles; flux growth
yields corundum and alexandrite whose wispy flux veils and platinum platelets can
mimic natural fingerprints; hydrothermal growth, used for emerald and quartz, leaves
seed plates and chevron zoning; and CVD or HPHT synthesis grows laboratory diamonds
requiring photoluminescence spectroscopy or DiamondView imaging for definitive
separation. A Chatham flux-grown ruby tests at the same refractive index (1.762–1.770)
and specific gravity (~4.00) as a Burmese stone, yet microscopy reveals flux
inclusions and metallic platelets absent from any natural ruby. Advanced laboratory
testing is required before issuing any identification report for high-value
synthetic material.
Flame Fusion (Verneuil Process)
Invented in 1902, this is the oldest and most economical method [1].
Powdered chemicals are dropped through a high-temperature flame, melting and crystallizing on a
rotating pedestal.
| Feature | Description |
|---|---|
| Curved striae | Diagnostic curved growth lines (vs. straight in natural) [2] |
| Gas bubbles | Spherical or elongated bubbles |
| Colour | Often more uniform than natural |
| Growth rate | Fast (hours to days) |
Flux Growth
Crystals grow slowly from a molten flux solution at high temperatures. This produces
high-quality crystals with natural-looking inclusions [3].
| Feature | Description |
|---|---|
| Flux inclusions | Wispy veils, fingerprints, flux "pools" [3] |
| Metallic platelets | Platinum or gold from crucible |
| Colour zoning | May be present but different pattern from natural |
| Growth rate | Slow (months) |
Notable Producers
- Chatham - Emerald, ruby, sapphire, alexandrite
- Ramaura - Ruby (very natural-looking)
- Kashan - Ruby
- Kyocera (Inamori) - Emerald, ruby
Hydrothermal Growth
Crystals grow in high-pressure aqueous solutions, mimicking natural conditions.
Used primarily for quartz and emerald.
Czochralski (Pulling) Method
A seed crystal is dipped into molten material and slowly pulled upward, growing
a single crystal. Used mainly for technical applications and some gem materials.
- YAG (yttrium aluminium garnet) - diamond simulant
- GGG (gadolinium gallium garnet) - diamond simulant
- Alexandrite (Czochralski and floating zone)
CVD and HPHT Diamond
Lab-grown diamonds are produced by two main methods. CVD and HPHT diamonds cannot be
detected without spectroscopy [5] [6].
HPHT (High Pressure High Temperature)
- Mimics natural diamond formation
- Metallic flux catalyst
- Often yellow tint (nitrogen)
- Metallic inclusions possible
- Strong magnetic under UV
CVD (Chemical Vapour Deposition)
- Carbon deposited from gas
- Lower pressure process
- Often brown (can be HPHT treated)
- Striated growth patterns
- May show weak fluorescence
Lab Diamond Detection
- DiamondView imaging (growth patterns)
- Photoluminescence spectroscopy
- UV-Vis-NIR spectroscopy
- Infrared spectroscopy (nitrogen patterns)
- Magnetic testing (HPHT metallic inclusions)
Detection Summary by Method
| Method | Key Detection Features |
|---|---|
| Flame Fusion | Curved striae, gas bubbles, uniform colour |
| Flux | Flux inclusions, metallic platelets, flux fingerprints |
| Hydrothermal | Seed plate, chevron zoning, nail-head spicules |
| Czochralski | Clean crystals, striae parallel to growth direction |
| HPHT Diamond | Metallic inclusions, strong fluorescence patterns |
| CVD Diamond | Striated growth, weak fluorescence, spectral features |
Common Simulants
| Simulated Gem | Common Simulants | Detection |
|---|---|---|
| Diamond | CZ, moissanite, white sapphire | Thermal/electrical conductivity, doubling (moissanite) |
| Ruby | Red glass, garnet, red spinel | RI, spectrum, inclusions |
| Emerald | Green glass, green tourmaline, tsavorite | RI, spectrum, Chelsea filter reaction |
| Sapphire | Blue glass, blue spinel, tanzanite | RI, spectrum, pleochroism |
Professional Testing
Historical Timeline
The development of synthetic gems spans over a century, with continuous advances
in quality and variety.
| Year | Development | Significance |
|---|---|---|
| 1902 | Verneuil (flame fusion) process | First commercial synthetic ruby |
| 1917 | Czochralski pulling method | Single crystals from melt |
| 1928 | Flux-grown emerald (IG Farben) | First synthetic emerald |
| 1953 | HPHT diamond (GE) | First reproducible synthetic diamond |
| 1963 | Chatham flux-grown ruby | Commercial flux synthetics |
| 1965 | Linde star sapphire | Synthetic star corundum |
| 1970s | Hydrothermal emerald | Emeralds with natural-like inclusions |
| 1980s | CVD diamond | Low-pressure diamond synthesis |
| 1990s | Tairus/Biron emerald | High-quality hydrothermal emerald |
| 2000s | Gem-quality HPHT diamond | Large, colourless diamonds |
| 2010s | Commercial CVD diamond | Widespread availability |
| 2020s | Affordable large lab diamonds | Market transformation |
Synthetic Moissanite
Synthetic moissanite (SiC, silicon carbide) is an important diamond simulant
discovered to have gem potential in the 1990s.
Properties
| Property | Moissanite | Diamond |
|---|---|---|
| Chemical formula | SiC | C |
| Crystal system | Hexagonal | Cubic |
| Refractive index | 2.65-2.69 | 2.417 |
| Birefringence | 0.043 (high) | None (isotropic) |
| Dispersion | 0.104 | 0.044 |
| Hardness | 9.25-9.5 | 10 |
| Specific gravity | 3.21 | 3.52 |
| Thermal conductivity | High (490 W/m·K) | Very high (2000+ W/m·K) |
Detection Methods
Moissanite can be distinguished from diamond by:
- Doubling: Strong birefringence shows facet doubling under magnification
- Electrical conductivity: Moissanite conducts; diamond doesn't (except Type IIb)
- Specific gravity: Lower than diamond (floats in 3.32 heavy liquid)
- Needle-like inclusions: White, parallel needles common
- Thermal-electrical testers: Dual-function testers identify moissanite
Market Position
Moissanite occupies a niche market:
- Marketed as alternative to diamond, not simulant
- Priced below diamond but above CZ
- Ethical/environmental positioning
- Own identity rather than diamond imitation
Synthetic Alexandrite
Synthetic alexandrite (colour-change chrysoberyl) is produced primarily by the
Czochralski pulling method and flux growth.
Production Methods
| Method | Characteristics | Detection Features |
|---|---|---|
| Czochralski | Clean crystals, strong colour change | Very clean; may have curved striae |
| Floating zone | Similar to Czochralski | Exceptionally clean |
| Flux growth | Natural-looking inclusions | Flux veils, metallic platelets |
Comparison with Natural
Natural alexandrite is extremely rare; most "alexandrite" in the market is synthetic
or colour-change sapphire.
Natural alexandrite features:
- Chrysoberyl inclusions
- Three-phase inclusions
- Irregular colour distribution
Synthetic alexandrite features:
- Very clean (Czochralski)
- Flux inclusions if flux-grown
- Strong, consistent colour change
Lab-Grown Diamond Market Evolution
The lab-grown diamond market has transformed dramatically, affecting both pricing
and consumer perception.
Market Trends
Price evolution:
- 2015: Lab-grown ~30-40% below mined equivalent
- 2020: ~50-70% below mined equivalent
- 2024: ~80-90% below mined equivalent (some sizes/qualities)
Market share:
- Growing rapidly in engagement ring market
- Dominant in industrial applications
- Increasing acceptance for fashion jewellery
Consumer Considerations
Disclosure Requirements
Lab-grown diamonds must be disclosed at every transaction:
- FTC (USA): "Laboratory-grown," "laboratory-created," or "[manufacturer name]-created"
- CIBJO: "Synthetic" or "laboratory-grown" with material name
- ISO 18323: Standard terminology for diamond industry
Terms like "cultured diamond" are discouraged to avoid pearl confusion.
Emerging Synthetics
New synthetic materials continue to enter the market.
Recent Developments
| Material | Status | Notes |
|---|---|---|
| Lab-grown padparadscha | Commercial | Flux and Czochralski methods |
| Synthetic Paraíba tourmaline | Limited | Copper-bearing tourmaline |
| Lab-grown spinel | Increasing | Flame fusion and flux |
| Synthetic demantoid | Research | Limited commercial availability |
Future Considerations
Gemmologists should anticipate:
- Continued improvement in synthetic quality
- New materials entering the market
- Evolution of detection methods
- Changing market dynamics and pricing
- Updated disclosure regulations
References
- ↑ 1. Nassau, K. (1980). Gems Made by Man. Chilton Book Company. ISBN: 978-0-8019-6773-8.
- ↑ 2. Read, P. (2014). Gemmology (3rd ed.). Butterworth-Heinemann. DOI: 10.4324/9780080507224.
- ↑ 3. Gübelin, E.; Koivula, J. (1986). Photoatlas of Inclusions in Gemstones, Vol. 1. ABC Edition Zürich. ISBN: 978-3-7281-2202-3.
- ↑ 4. Gübelin, E.; Koivula, J. (1992). Photoatlas of Inclusions in Gemstones, Vol. 2. ABC Edition Zürich.
- ↑ 5. Martineau, P. (2004). Identification of Synthetic Diamond Grown Using Chemical Vapor Deposition (CVD). Gems & Gemology, 40(1). DOI: 10.5741/gems.40.1.2.
- ↑ 6. Eaton-Magaña, S. (2017). An Introduction to CVD-Grown Synthetic Diamond. Gems & Gemology, 53(3). DOI: 10.5741/gems.53.3.262.