Field report · 969
Inclusions are not flaws: what they tell you
The bubbles, needles, and clouds inside a stone are its fingerprint. Here's how to read them.
One of the biggest mindset shifts when you start buying colored stones is realizing that inclusions — the internal features that diamond grading penalizes — are actually how you authenticate and locate the stone. "Eye-clean" is good. "Perfectly clean" is suspicious.
What inclusions are
An inclusion is anything inside the crystal that isn't the host mineral. Inclusions form during the stone's growth and freeze in place as it cools. Common types:
- Solid inclusions — small crystals of other minerals that grew alongside
- Liquid / fluid inclusions — tiny pockets of water or other fluids trapped during growth
- Gas inclusions — bubbles, often inside fluid inclusions ("two-phase" or "three-phase")
- Healing features — internal fractures that re-healed during growth, leaving wispy patterns
- Color zones — bands of different color showing growth phases
What inclusions tell a gemologist
Trained eyes can read inclusions like a passport:
- Silk inclusions (fine rutile needles) — typical of corundum (sapphire/ruby). Sri Lankan sapphire has different silk patterns than Burmese.
- Three-phase inclusions (solid + liquid + gas) — diagnostic of emerald from Colombia.
- Horsetail inclusions (radiating chrysotile fibers) — diagnostic of Russian demantoid garnet.
- Liquid feathers / fingerprints — show whether a stone has been heated (heat changes the pattern)
- Negative crystals (geometric voids) — common in natural stones, rare in synthetics
Why "perfectly clean" is a yellow flag
Natural stones almost always contain some internal evidence of their growth — even at the highest grades, gemologists can find inclusions under magnification. A stone with absolutely no internal features under 10x magnification is one of three things:
- Synthetic (lab-grown stones have different inclusion patterns; sometimes none visible)
- Glass imitation
- Very small (under 0.5ct, where inclusions may not be visible without a microscope)
For premium colored stones, the lab report often describes the inclusion type as a positive ID. "Silk inclusions consistent with natural origin" or "three-phase inclusions consistent with Colombian origin" is the lab telling you exactly why they identify the stone as natural and from that locality.
What to look for
Use a 10x loupe (the standard gemologist's tool, $15-30 online):
- Natural-looking inclusions — random distribution, mineral crystals, fluid features
- NOT synthetic indicators — curved growth lines (synthetic sapphire), gas bubbles in glass, perfectly geometric "flux" inclusions in some synthetics
- Stable inclusions — solid mineral inclusions are fine; surface-reaching fractures need disclosure (often oiled)
The collector mindset: inclusions are part of what makes a natural stone not interchangeable. They're the stone's birth certificate.