--- name: identify-gemstone locale: caveman-lite source_locale: en source_commit: 82c77053 translator: "Julius Brussee homage — caveman" translation_date: "2026-04-24" description: > Identify gemstones using optical properties, physical tests, and inclusion analysis. Covers refractive index, specific gravity, pleochroism, spectroscopy indicators, and common simulant detection. Use when identifying an unknown gemstone, verifying a seller's claim about species identity, distinguishing natural stones from simulants or synthetics, building gemological literacy through structured observation, or identifying rough material before cutting to ensure safe handling. license: MIT allowed-tools: Read metadata: author: Philipp Thoss version: "1.0" domain: lapidary complexity: intermediate language: natural tags: lapidary, gemstones, identification, mineralogy, optics --- # 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 **Got:** A complete visual profile including colour, transparency, luster, and any phenomena. This alone narrows candidates to a manageable shortlist. **If fail:** 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 **Got:** 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. **If fail:** 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 **Got:** RI value (to 0.001), birefringence, optic character, pleochroism description, and UV response. Combined with Step 2, this identifies most gemstone species definitively. **If fail:** 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 **Got:** 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). **If fail:** 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 **Got:** 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. **If fail:** 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) ## Pitfalls - **Trusting colour alone**: Colour is the least reliable identification property. Blue stones include sapphire, topaz, aquamarine, tanzanite, iolite, spinel, glass, and CZ. 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