Identify Gemstone

Identify gemstones using systematic physical and optical property testing, inclusion analysis, and elimination against known species profiles.

When to Use

• You have an unknown gemstone or suspect gemstone and want to identify the species
• You need to verify a seller's claim about a gemstone's identity
• You want to distinguish a natural gemstone from a common simulant or synthetic
• You are building gemological literacy through structured observation and testing
• You need to identify rough material before cutting to ensure safe handling

Inputs

• Required: A gemstone specimen (loose stone preferred; mounted stones limit testing)
• Optional: Refractometer with contact liquid (RI fluid, 1.81 standard)
• Optional: Dichroscope (for pleochroism testing)
• Optional: Chelsea colour filter
• Optional: Specific gravity balance or heavy liquids
• Optional: 10x loupe or gemological microscope
• Optional: UV lamp (long-wave 365nm and short-wave 254nm)
• Optional: Polariscope (for optic character determination)

Procedure

Step 1: Visual Inspection

Examine the specimen with the unaided eye and then under 10x magnification.

Visual Inspection Checklist:
+--------------------+------------------------------------------+
| Observation        | Record                                   |
+--------------------+------------------------------------------+
| Colour             | Hue (red, blue, green...), saturation    |
|                    | (vivid, moderate, weak), tone            |
|                    | (light, medium, dark)                    |
+--------------------+------------------------------------------+
| Transparency       | Transparent, translucent, opaque         |
+--------------------+------------------------------------------+
| Luster             | Adamantine, vitreous, waxy, pearly,      |
|                    | silky, resinous                          |
+--------------------+------------------------------------------+
| Cut style          | Faceted, cabochon, carved, rough         |
+--------------------+------------------------------------------+
| Estimated size     | Approximate dimensions (mm) and weight   |
+--------------------+------------------------------------------+
| Surface condition  | Scratches, chips, abrasion, wear pattern |
+--------------------+------------------------------------------+
| Phenomena          | Star (asterism), cat's eye               |
|                    | (chatoyancy), play of colour, colour     |
|                    | change, adularescence                    |
+--------------------+------------------------------------------+

1. Note the body colour under daylight-equivalent lighting (5500-6500K)
2. Check for colour zoning by viewing through the stone from different angles
3. Assess transparency and luster — these narrow the candidate list immediately
4. Look for optical phenomena (star, cat's eye, play of colour)
5. Record any visible inclusions without magnification

Expected: A complete visual profile including colour, transparency, luster, and any phenomena. This alone narrows candidates to a manageable shortlist.

On failure: If lighting is poor (yellowish indoor light), note the limitation. Daylight or daylight-equivalent bulbs are strongly preferred. Incandescent light shifts colour perception and can cause misidentification of colour-change stones.

Step 2: Physical Property Testing

Test measurable physical properties to narrow the identification.

Key Physical Properties:
+--------------------+------------------------------------------+
| Property           | Method                                   |
+--------------------+------------------------------------------+
| Hardness (Mohs)    | Scratch test against reference minerals  |
|                    | or hardness pencils. CAUTION: Do NOT     |
|                    | scratch faceted gemstones — use other    |
|                    | tests instead for cut stones             |
+--------------------+------------------------------------------+
| Specific gravity   | Hydrostatic weighing:                    |
| (SG)               | SG = weight in air / (weight in air -    |
|                    | weight in water)                         |
|                    |                                          |
|                    | Common SG values:                        |
|                    | Quartz: 2.65                             |
|                    | Beryl: 2.68-2.74                         |
|                    | Tourmaline: 3.02-3.26                    |
|                    | Topaz: 3.53                              |
|                    | Corundum: 3.99-4.01                      |
|                    | Zircon: 4.60-4.73                        |
|                    | CZ: 5.65-5.95                            |
+--------------------+------------------------------------------+
| Heft               | Does the stone feel heavier or lighter   |
|                    | than expected for its size?              |
|                    | CZ and zircon feel noticeably heavy      |
|                    | Quartz and glass feel average            |
+--------------------+------------------------------------------+

1. For rough material: test hardness using Mohs scale reference points
2. For cut stones: measure specific gravity using hydrostatic method
3. Assess heft — experienced handlers can distinguish CZ from diamond by weight alone
4. Note any cleavage planes visible on the surface

Expected: Hardness range (for rough) or SG value (for cut stones) that differentiates between candidate species. SG is often the most powerful single diagnostic for cut stones.

On failure: If hydrostatic balance is unavailable, use the heft test as a rough guide. Stones that feel "too heavy for their size" likely have high SG (>3.5). If hardness testing would damage a cut stone, skip to optical tests.

Step 3: Optical Tests

Apply gemological optical instruments for definitive properties.

Optical Property Tests:
+--------------------+------------------------------------------+
| Test               | What It Reveals                          |
+--------------------+------------------------------------------+
| Refractive Index   | Measured on refractometer with RI fluid  |
| (RI)               | Diagnostic for most species:             |
|                    | Quartz: 1.544-1.553                      |
|                    | Beryl: 1.577-1.583                       |
|                    | Tourmaline: 1.624-1.644                  |
|                    | Topaz: 1.609-1.617                       |
|                    | Corundum: 1.762-1.770                    |
|                    | Spinel: 1.718                            |
|                    | Diamond: 2.417 (OTL on refractometer)    |
|                    | CZ: 2.15 (OTL on refractometer)          |
+--------------------+------------------------------------------+
| Birefringence      | Difference between high and low RI       |
| (BR)               | Quartz: 0.009                            |
|                    | Corundum: 0.008                          |
|                    | Tourmaline: 0.018-0.020                  |
|                    | Singly refractive: 0 (spinel, garnet,    |
|                    | diamond)                                 |
+--------------------+------------------------------------------+
| Pleochroism        | Colour variation with crystal direction  |
| (dichroscope)      | Strong: tourmaline, tanzanite, iolite    |
|                    | Moderate: corundum, topaz                |
|                    | None: singly refractive stones           |
+--------------------+------------------------------------------+
| Optic character    | Singly refractive (SR), doubly           |
| (polariscope)      | refractive (DR), aggregate (AGG)         |
+--------------------+------------------------------------------+
| UV fluorescence    | Long-wave and short-wave UV response     |
|                    | Diamond: often blue (LWUV)               |
|                    | Ruby: strong red (LWUV)                  |
|                    | Emerald: usually inert                   |
+--------------------+------------------------------------------+
| Chelsea filter     | Transmits deep red and yellow-green      |
|                    | Emerald (Cr): appears red/pink           |
|                    | Aquamarine: appears green                |
|                    | Blue synthetic spinel: appears red       |
+--------------------+------------------------------------------+

1. Measure RI on refractometer — take both high and low readings for birefringence
2. Test pleochroism with dichroscope — rotate slowly and note colour changes
3. Check optic character on polariscope (SR vs DR vs AGG)
4. Test UV fluorescence under both long-wave and short-wave
5. Use Chelsea filter if chromium-coloured stones are suspected

Expected: RI value (to 0.001), birefringence, optic character, pleochroism description, and UV response. Combined with Step 2, this identifies most gemstone species definitively.

On failure: If RI is over-the-limit (OTL, >1.81), the stone is likely diamond, CZ, zircon (high-type), or a high-RI synthetic. Use SG and thermal conductivity to differentiate. If no refractometer is available, rely on SG + visual properties + inclusions.

Step 4: Inclusion Analysis

Examine internal features under magnification for species confirmation and natural vs. synthetic determination.

Diagnostic Inclusions by Species:
+------------------+------------------------------------------+
| Species          | Characteristic Inclusions                |
+------------------+------------------------------------------+
| Diamond          | Crystals (garnet, diopside), feathers,   |
|                  | cloud, graining, pinpoints               |
+------------------+------------------------------------------+
| Ruby/Sapphire    | Silk (rutile needles), fingerprints,     |
|                  | colour zoning (straight angular),        |
|                  | crystal inclusions                       |
+------------------+------------------------------------------+
| Emerald          | Three-phase inclusions (solid + liquid + |
|                  | gas), jardin (garden-like fractures),    |
|                  | pyrite crystals                          |
+------------------+------------------------------------------+
| Tourmaline       | Growth tubes, liquid-filled fractures    |
+------------------+------------------------------------------+
| Quartz/Amethyst  | Tiger stripes, phantoms, two-phase       |
|                  | inclusions, negative crystals            |
+------------------+------------------------------------------+

Synthetic Indicators:
+------------------+------------------------------------------+
| Synthetic Type   | Telltale Inclusions                      |
+------------------+------------------------------------------+
| Flame fusion     | Curved growth lines (striae),            |
| (Verneuil)       | gas bubbles (spherical)                  |
+------------------+------------------------------------------+
| Flux grown       | Flux fingerprints (wispy veils),         |
|                  | platinum platelets                       |
+------------------+------------------------------------------+
| Hydrothermal     | Chevron or zigzag growth patterns,       |
|                  | seed plate remnant                       |
+------------------+------------------------------------------+
| Glass simulants  | Round gas bubbles, swirl marks,          |
|                  | conchoidal fracture chips                |
+------------------+------------------------------------------+

1. Examine the stone under darkfield illumination (gemological microscope) or oblique lighting through a 10x loupe
2. Look for species-diagnostic inclusions first
3. Check for synthetic indicators — curved striae and gas bubbles are definitive for flame-fusion synthetics
4. Note the inclusion type, location, and frequency
5. Photograph inclusions if possible for records

Expected: Species-confirming inclusion pattern and natural/synthetic determination. Some species are identified more by their inclusions than by optical properties (e.g., emerald's jardin).

On failure: If the stone is eye-clean and no inclusions are visible at 10x, it may be a very clean natural stone or a synthetic. Lack of inclusions raises the synthetic probability — refer to optical and physical tests for confirmation. Laboratory analysis (FTIR, Raman) may be needed.

Step 5: Identification by Elimination

Cross-reference all collected data to reach a final identification.

1. Compile the property profile:
   • Colour + transparency + luster
   • Hardness or SG
   • RI + birefringence + optic character
   • Pleochroism + UV fluorescence
   • Inclusion pattern
2. Compare against reference tables for candidate species
3. Eliminate species that conflict with any measured property
4. If two or more candidates remain, identify the distinguishing test:
   • Example: blue topaz vs. aquamarine — SG is definitive (3.53 vs. 2.70)
5. State the identification with confidence level:
   • Definitive: Multiple properties confirm a single species
   • Probable: Properties consistent with one species, but one test missing
   • Uncertain: Conflicting data or insufficient testing — laboratory referral recommended

Expected: A final species identification (e.g., "Natural sapphire, blue, heat-treated") with supporting evidence from each test category. Or a clear recommendation for laboratory analysis if field tests are insufficient.

On failure: If the stone cannot be identified with available equipment, document all measured properties and refer to a gemological laboratory. Provide the measured data to the lab — it accelerates their analysis.

Validation

• Visual inspection completed under daylight-equivalent lighting
• At least two physical properties measured (hardness/SG + one other)
• RI measured and birefringence calculated (if refractometer available)
• Pleochroism tested (if dichroscope available)
• Inclusions examined under at least 10x magnification
• Identification reached by systematic elimination, not assumption
• Common simulants explicitly considered and ruled out
• Natural vs. synthetic determination made (or flagged as uncertain)

Common Pitfalls

• Trusting colour alone: Colour is the least reliable identification property. Blue stones include sapphire, topaz, aquamarine, tanzanite, iolite, spinel, glass, and CZ. Always confirm with measurable properties
• Skipping SG on mounted stones: Mounted stones limit testing, but you can still check RI, pleochroism, inclusions, and UV. Document the limitation rather than guessing
• Confusing high-RI synthetics with naturals: Flame-fusion rubies and sapphires have identical RI and SG to natural stones. Only inclusions (curved striae vs. straight growth) differentiate them
• Assuming expensive = natural: Commercial jewellery frequently contains treated, synthetic, or simulant stones. Test every stone regardless of provenance claims
• Damaging the specimen: Never hardness-test a faceted gemstone — it will leave visible scratches. Use non-destructive tests (RI, SG, inclusions) for cut stones

Related Skills

• cut-gemstone

  — Identification determines safe cutting parameters and orientation requirements for the species

• appraise-gemstone

  — Positive identification is the prerequisite for any meaningful valuation

• mineral-identification

  — Field mineral identification methodology using physical properties (prospecting domain) shares the systematic elimination approach