Knowledge Modules¶
The Gemmology Knowledge repository contains 13 comprehensive knowledge modules covering core gemmological topics.
Physical Properties¶
Hardness, specific gravity, crystal systems, cleavage, fracture, and lustre
Understanding physical properties is fundamental to gem identification. This module covers:
- Mohs Hardness Scale: The 10-point comparative hardness scale
- Specific Gravity (SG): Density measurement techniques and values
- Crystal Systems: The 7 crystal systems and 32 point groups
- Cleavage: Atomic planes of weakness and their gem significance
- Fracture: Non-directional breaking patterns
- Lustre: Surface light reflection characteristics
Key Concepts¶
| Property | Measurement | Significance |
|---|---|---|
| Hardness | Mohs scale 1-10 | Durability, cutting resistance |
| SG | Hydrostatic balance | Identification, authenticity |
| Cleavage | Miller indices | Setting considerations |
Optical Properties¶
Refractive index, birefringence, pleochroism, dispersion, and spectroscopy
Optical properties are the primary means of gem identification. This module covers:
- Refractive Index (RI): Light bending measurement
- Birefringence: Double refraction in anisotropic crystals
- Optical Character: Uniaxial vs. biaxial, positive vs. negative
- Pleochroism: Directional colour variation
- Dispersion: Spectral colour separation ("fire")
- Absorption Spectrum: Characteristic absorption bands
Refractometer Use¶
The refractometer is the most important gem testing instrument:
- Clean the gem and instrument
- Apply contact liquid (RI 1.81)
- Place gem on hemicylinder
- Read shadow edge position
Chemical Properties¶
Chemical composition, chromophores, trace elements, and colour causes
Understanding chemistry explains gem colours and properties:
- Chemical Formulas: Mineral compositions
- Chromophores: Colour-causing elements (Cr, Fe, Cu, Mn, V)
- Trace Elements: Minor impurities affecting colour
- Colour Centres: Radiation-induced colour
- Charge Transfer: Fe²⁺/Fe³⁺ and Ti⁴⁺ interactions
Common Chromophores¶
| Element | Colour | Example Gems |
|---|---|---|
| Cr³⁺ | Red, green | Ruby, emerald |
| Fe²⁺ | Blue, green | Aquamarine, peridot |
| Fe³⁺ | Yellow | Citrine, yellow sapphire |
| Cu²⁺ | Blue, green | Turquoise, Paraíba tourmaline |
| Mn³⁺ | Pink, red | Kunzite, rhodonite |
Inclusions & Fingerprints¶
Internal features, diagnostic inclusions, growth patterns, and fingerprint identification
Inclusions are key to natural vs. synthetic determination:
- Crystal Inclusions: Trapped mineral crystals
- Fluid Inclusions: Two-phase and three-phase inclusions
- Growth Patterns: Zoning, phantoms, twinning
- Fingerprint Inclusions: Partially healed fractures
- Diagnostic Inclusions: Species-specific features
Diagnostic Examples¶
| Inclusion | Gem | Significance |
|---|---|---|
| Silk | Ruby, sapphire | Natural corundum |
| Three-phase | Colombian emerald | Origin indicator |
| Horsetail | Demantoid garnet | Russian origin |
| Rain | Peridot | Natural origin |
Gem Testing Instruments¶
Refractometer, spectroscope, polariscope, dichroscope, Chelsea filter, UV lamp, and microscopy
Proper instrument use is essential for accurate identification:
- Refractometer: RI and birefringence measurement
- Spectroscope: Absorption spectrum observation
- Polariscope: Optical character determination
- Dichroscope: Pleochroism observation
- Chelsea Filter: Emerald/green stone separation
- UV Lamp: Fluorescence observation
- Microscope: Inclusion study
Treatments & Enhancements¶
Heat treatment, diffusion, filling, coating, irradiation, and treatment detection
Most gems undergo some form of treatment:
- Heat Treatment: Colour modification, clarity improvement
- Beryllium Diffusion: Lattice diffusion of Be
- Fracture Filling: Glass, oil, resin filling
- Surface Coating: Thin film enhancements
- Irradiation: Colour creation/modification
- HPHT: Diamond colour modification
Detection Methods¶
| Treatment | Detection Method |
|---|---|
| Heat | Inclusion changes, spectroscopy |
| Diffusion | Immersion, concentration patterns |
| Filling | Magnification, flash effects |
| Coating | Surface examination |
| Irradiation | Spectroscopy, colour zoning |
Synthetics & Simulants¶
Flame fusion, hydrothermal, flux growth, CVD/HPHT, and synthetic identification
Distinguishing natural from synthetic is crucial:
- Flame Fusion (Verneuil): Curved striae, gas bubbles
- Hydrothermal: Seed plates, nail-head inclusions
- Flux Growth: Flux inclusions, colour zoning
- CVD Diamond: Distinctive growth patterns
- HPHT Diamond: Colour zoning, metallic inclusions
Gemstone Species¶
Detailed profiles for 50+ gem species and varieties
Comprehensive data on major gem species:
- Corundum: Ruby, sapphire varieties
- Beryl: Emerald, aquamarine, morganite
- Chrysoberyl: Alexandrite, cat's eye
- Garnet Group: Pyrope, almandine, spessartine, grossular, andradite
- Tourmaline Group: Elbaite, liddicoatite, dravite
- Quartz Group: Amethyst, citrine, smoky, rose
- Feldspar Group: Moonstone, labradorite, sunstone
- And many more...
Grading & Valuation¶
Colour grading (hue, tone, saturation), clarity, cut quality, and value factors
Understanding how gems are evaluated:
- Colour Grading: Hue, tone, saturation system
- Clarity Grading: Inclusion visibility scales
- Cut Quality: Proportions, symmetry, polish
- Carat Weight: Size-value relationships
- Market Factors: Rarity, demand, origin premiums
Gem Care & Durability¶
Stability, cleaning methods, setting recommendations, and storage
Proper gem care ensures longevity:
- Stability: Heat, light, chemical sensitivity
- Cleaning Methods: Safe cleaning by gem type
- Setting Recommendations: Appropriate settings for hardness/cleavage
- Storage: Preventing damage and contamination
Cleaning Guide¶
| Gem Type | Safe Methods | Avoid |
|---|---|---|
| Diamond | Ultrasonic, steam | - |
| Ruby/Sapphire | Ultrasonic, steam | - |
| Emerald | Warm soapy water | Ultrasonic, steam |
| Pearl | Damp cloth | Chemicals, ultrasonic |
| Opal | Damp cloth | Heat, ultrasonic |
Origin Determination¶
Geographic origin characteristics, provenance, and origin premiums
Origin can significantly affect value:
- Inclusion Suites: Origin-specific inclusion assemblages
- Trace Elements: Geographic chemical signatures
- Spectroscopy: Origin-related absorption features
- Premium Origins: Kashmir, Burma, Colombia, Paraíba
Phenomenal Gems¶
Asterism, chatoyancy, adularescence, labradorescence, play of colour, and colour change
Special optical phenomena in gems:
- Asterism: Star effect (ruby, sapphire)
- Chatoyancy: Cat's eye effect (chrysoberyl)
- Adularescence: Floating light (moonstone)
- Labradorescence: Spectral colours (labradorite)
- Play of Colour: Spectral flashes (opal)
- Colour Change: Alexandrite effect
Crystal Visualization¶
CDL notation, crystal morphology, Miller indices, and 3D visualization
Understanding crystal forms aids identification:
- CDL Notation: Crystal Description Language syntax
- Crystal Systems: 7 systems and their characteristics
- Miller Indices: Face notation system
- Point Groups: 32 crystallographic symmetries
- Crystal Habits: Common morphologies by species
- Twinning: Contact and penetration twins