Synthetic Gemstones
Synthetic gem production methods including flame fusion, hydrothermal, flux growth, and detection techniques.
Introduction
Synthetic gems have the same chemical composition, crystal structure, and physical
properties as their natural counterparts. They are created in laboratories using
various growth methods.
Flame Fusion (Verneuil Process)
Invented in 1902, this is the oldest and most economical method. 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) |
| 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.
| Feature | Description |
|---|---|
| Flux inclusions | Wispy veils, fingerprints, flux "pools" |
| 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.
| Feature | Description |
|---|---|
| Seed plate | Visible seed crystal or growth boundary |
| Chevron zoning | Zigzag or V-shaped colour patterns |
| Nail-head spicules | Characteristic pointed inclusions |
| Two-phase inclusions | Different appearance from natural |
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.
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