Natural vs Synthetic Indicators

Inclusions provide the most accessible evidence for distinguishing natural gemstones
from their synthetic counterparts. Although a laboratory-grown ruby shares the same
refractive index, specific gravity, and chemical composition as a Burmese stone,
its formation conditions differ profoundly, leaving characteristic internal signatures
readable under the microscope. Natural crystals grow slowly in complex geological
fluids, accumulating mineral guests, multi-phase fluid inclusions, irregular colour
zoning, and healing fractures that no synthetic process replicates faithfully.
Synthetics carry the hallmarks of their growth method: curved striae and spherical
gas bubbles in flame-fusion corundum; wispy flux veils and platinum platelets in
flux-grown ruby; seed plates and chevron zoning in hydrothermal emerald ^[1].
The practical stakes are high: flame-fusion synthetic sapphire may retail for
under a dollar per carat, while a fine Kashmir natural commands tens of thousands.
Microscopic examination at 40–60× under darkfield and immersion is the first and
most cost-effective step before committing to spectroscopic analysis.

Flame fusion is the oldest and most common method for synthetic corundum and spinel.
Curved striae are the most diagnostic feature ^[2]:

Characteristic inclusions:

• Curved striae - Curved growth lines (most diagnostic) ^[2]
• Gas bubbles - Round or elongated bubbles, often in strings
• Unmelted powder - Rare, small grains of starting material

Observation tips:

• Curved striae best seen with immersion and polarized light
• Bubbles may be very small - use high magnification
• Striae follow the curved boule shape

Flux-grown synthetics crystallize from a molten flux solution. Key features include
platinum/gold flakes, fine feathers, and wispy veils ^[1]:

Characteristic inclusions:

• Flux inclusions - Wispy, veil-like, or fingerprint-like patterns ^[1]
• Platinum/gold flakes - Metallic crucible remnants
• Flux residue - Glassy or crystalline flux material
• Seed remnants - If grown on a seed crystal

Important distinctions:

• Flux inclusions can resemble natural fingerprints
• Look for metallic flakes (not present in nature)
• Flux has distinctive appearance different from natural fluids

Hydrothermal synthetics grow from aqueous solutions at high pressure.
Chevron/zigzag zoning and seed plates are diagnostic ^[3]:

Characteristic inclusions:

• Chevron/zigzag zoning - Distinctive angular growth patterns ^[3]
• Seed plate - Remnant of the seed crystal
• Breadcrumb inclusions - Small, white, scattered particles
• Nail-head spicules - Elongated, pointed inclusions

Common hydrothermal synthetics:

• Synthetic emerald (Biron, Tairus, Russian)
• Synthetic quartz (most common method)
• Some synthetic corundum

Lab-grown diamonds require special attention. CVD and HPHT diamonds cannot be
identified without spectroscopic analysis ^{[4] [5]}.

HPHT (High Pressure High Temperature):

• Metallic flux inclusions (Fe, Ni, Co)
• Cross-shaped or irregular patterns
• Strong magnetism possible
• Distinctive fluorescence patterns

CVD (Chemical Vapor Deposition):

• Often very clean
• May show strain patterns
• Point defects from process
• Distinctive spectroscopy features

Synthetic spinel is commonly produced by flame fusion:

Key features:

• Gas bubbles - Very common, often in clouds or strings
• Curved striae - Similar to synthetic corundum
• Anomalous double refraction (ADR) - Strong strain patterns
• High clarity - Often cleaner than natural

Some cases require advanced testing beyond microscopy:

Challenging scenarios:

• Very clean natural stones with few inclusions
• High-quality flux synthetics
• CVD diamonds (often very clean)
• Treated naturals with altered inclusions

Additional testing methods:

• Spectroscopy (FTIR, Raman, UV-Vis)
• Fluorescence imaging
• Trace element analysis
• Photoluminescence mapping

When microscopic evidence is inconclusive, always recommend advanced testing
by a qualified gemmological laboratory.