Natural vs Synthetic Indicators

Inclusions provide crucial evidence for distinguishing natural gemstones from
their synthetic counterparts. While synthetics may have the same chemical
composition and crystal structure, their formation conditions differ dramatically,
leaving characteristic internal features.

Flame fusion is the oldest and most common method for synthetic corundum and spinel:

Characteristic inclusions:

• Curved striae - Curved growth lines (most diagnostic)
• 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:

Characteristic inclusions:

• Flux inclusions - Wispy, veil-like, or fingerprint-like patterns
• 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:

Characteristic inclusions:

• Chevron/zigzag zoning - Distinctive angular growth patterns
• 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:

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.