How to identify gemstones
A structured FGA-aligned diagnostic workflow, free
Reliable gemstone identification is a sequential elimination problem rather than a single test: an unknown stone is rarely identifiable from any one measurement alone, but the intersection of refractive index, specific gravity, optic character, pleochroism, absorption spectrum, fluorescence response, and the microscopic inclusion suite narrows almost every gem species to a unique match. This hub walks the standard nine-step protocol used in FGA laboratory practice and links to the 15 supporting articles covering inclusions, treatments, synthetics, and composite-stone diagnosis. Every test below is supported by an interactive browser calculator (refractometer simulator, SG calculator with water-temperature correction, spectroscope band-matcher, treatment wizard, optic-sign reasoner) so that theory and applied technique stay paired. If you are revising for the Gem-A Foundation or Diploma examinations, start with the diagnostic-procedure table, then drill into the inclusion atlas (six sub-articles) and the treatment / synthetics deep dives.
The nine-step identification protocol
| Step | Test | What it tells you | Tool |
|---|---|---|---|
| 1 | Visual observation | Colour, transparency, lustre, polish quality, surface features | Loupe (10×) or low-power microscope |
| 2 | Refractive index | Narrow species shortlist; isotropic vs anisotropic; birefringence | Standard refractometer + sodium light + RI liquid (n=1.81) |
| 3 | Specific gravity | Confirm species or separate same-RI candidates (e.g. emerald vs aquamarine) | Hydrostatic balance or heavy liquids (di-iodomethane, bromoform) |
| 4 | Polariscope | Optic character: singly refractive, doubly refractive, ADR, aggregate | Crossed polars + conoscope attachment for interference figures |
| 5 | Dichroscope | Pleochroism colours and intensity; diagnostic for ruby, tanzanite, iolite, andalusite | Calcite or polarising-film dichroscope |
| 6 | Spectroscope | Absorption-band pattern: chromium, iron, manganese, rare-earth signatures | Hand or prism-stand spectroscope with strong transmitted light |
| 7 | UV fluorescence | LWUV / SWUV response; separates natural from synthetic and origins | LWUV (365 nm) + SWUV (254 nm) lamp; dark cabinet |
| 8 | Microscopic inspection | Inclusion suite, growth structure, curved striae, treatment evidence | Gemmological microscope with darkfield + diffused transmitted lighting |
| 9 | Advanced lab | FTIR, Raman, UV-Vis-NIR, LIBS, photoluminescence for origin and treatment work | Submission to gem laboratory (GIA, SSEF, Gübelin, GRS, GIT) |
Try the workflow against an unknown stone using the Gem Identifier, which filters the mineral database by the measurements you enter.
Identification fundamentals
Beryllium Diffusion: Deep Diagnostic Reference
Full per-method detection protocol for beryllium lattice diffusion in corundum, with disclosure standards and stability data.
advancedComposite Stones
Doublets, triplets, assembled stones, and their detection including opal doublets, garnet-topped doublets, and soudé emeralds.
intermediateCVD Diamond Detection: Deep Diagnostic Reference
Full detection protocol for CVD synthetic diamonds, distinguishing from natural and HPHT-treated stones using DiamondView, FTIR, and photoluminescence.
advancedGemstone Treatments
Heat treatment, filling, diffusion, coating, and detection methods for treated gemstones, with per-species diagnostic depth.
intermediateHPHT Diamond Treatment: Deep Diagnostic Reference
Full detection protocol for HPHT-treated natural diamonds, including type-by-type outcomes, DiamondView patterns, and photoluminescence signatures.
advancedLead Glass-Filled Ruby: Deep Diagnostic Reference
Full detection protocol for composite (lead glass-filled) ruby, with nomenclature, durability, and disclosure standards.
advancedSynthetic Gemstones
Synthetic gem production methods including flame fusion, hydrothermal, flux growth, and detection techniques.
advancedInclusions atlas
(8 articles)Feathers & Fingerprints
Healed fractures, fingerprint inclusions, and liquid feathers - characteristic healing patterns in gems.
Fluid Inclusions
Two-phase, three-phase, and negative crystal inclusions - trapped fluids that reveal formation conditions.
Growth Features
Colour zoning, growth tubes, twinning, phantoms, and other patterns formed during crystallization.
Inclusions Overview
Introduction to inclusions, their classification, and microscopy techniques for examination.
Natural vs Synthetic Indicators
Distinguishing natural gemstones from synthetics using inclusion evidence.
Silk & Needle Inclusions
Rutile silk, needle inclusions, and their role in asterism and origin determination.
Solid Inclusions
Crystal inclusions - identifying mineral guests trapped within gemstones during formation.
Surface Features
Naturals, bearding, etch channels, and other surface-related inclusion features.
Hands-on companion tools
Each step in the protocol above has an interactive widget on this site that runs entirely in your browser (no installation, no account, no upload of stone data):
- Measurement : RI lookup, SG with water-temp correction, birefringence, carat estimator
- Optical : refractometer simulator, polariscope guide, pleochroism + optic-sign reasoners
- Lab : spectroscope calculator + band-matcher, UV-fluorescence lookup
- Identification : Gem Identifier (filtered DB query against your measured RI/SG/system)
- Advanced : Treatment Wizard, Treatment Detection table, Proportion Analyzer
- Practice quiz : SM-2-scheduled spaced-repetition with rationale panels