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feat(learn): reorganize curriculum into 8-category structure
Expand from 3 broad categories to 8 specialized categories with 62 content files: - fundamentals/: Crystal systems, optical/physical/chemical properties (6 files) - equipment/: Individual pages for each instrument type (8 files) - species/: 19 gem species including organic gems (amber, coral, jet, pearl) - phenomena/: 9 optical phenomena (asterism, chatoyancy, play-of-colour, etc.) - origin/: 10 geographic sources (Burma, Kashmir, Colombia, Ceylon, etc.) - identification/: Inclusions, treatments, synthetics, composites (4 files) - market/: Grading, lab reports, disclosure, professional practice (4 files) - care/: Durability and care guidelines (1 file) Breaking changes: - Monolithic files split into individual topic pages - URL structure now uses category/topic paths (e.g., /learn/species/corundum) - Removed: gem-testing-instruments.yaml, phenomenal-gems.yaml, origin-determination.yaml, organic-gems.yaml This enables deeper content organization and better navigation for the FGA curriculum learning path.
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docs/learn/gem-care-durability.yaml renamed to docs/learn/care/gem-care-durability.yaml

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title: Gem Care and Durability
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description: Gemstone stability, cleaning methods, setting recommendations, storage guidelines, and jewellery suitability for different gem species.
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order: 11
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category: advanced
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category: care
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difficulty: beginner
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icon: shield
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related:

‎docs/learn/equipment/dichroscope.yaml‎

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title: The Dichroscope
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description: Using the dichroscope to observe pleochroism in coloured gemstones, distinguishing dichroic from trichroic materials.
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order: 4
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category: equipment
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difficulty: beginner
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icon: palette
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related:
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- optical-properties
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- index
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- polariscope
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tags:
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- dichroscope
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- pleochroism
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- colour
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- identification
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sections:
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- title: Introduction
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content: |
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The dichroscope reveals pleochroism by showing two polarised images side by side.
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It's essential for identifying coloured anisotropic gems and can help distinguish
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natural from synthetic materials.
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Pleochroism—the property of showing different colours in different crystallographic
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directions—is diagnostic for many coloured gemstones.
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- title: Types of Dichroscope
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content: |
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Two main types are available:
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subsections:
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- title: Calcite Dichroscope
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content: |
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Uses a calcite rhomb (Iceland spar) to split the image:
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- **More accurate**: Clear separation of colours
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- **Traditional choice**: Preferred by professionals
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- **Higher cost**: More expensive than polaroid type
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- **Fragile**: Calcite can cleave if dropped
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- title: Polaroid Dichroscope
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content: |
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Uses polarising film to create two windows:
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- **More affordable**: Lower cost option
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- **Durable**: Less fragile than calcite
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- **Good for field use**: Compact and rugged
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- **Slightly less clear**: Colours may be slightly muted
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- title: Usage Technique
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content: |
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Proper technique is essential for accurate results:
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subsections:
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- title: Basic Procedure
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content: |
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1. View the gem through the dichroscope with strong transmitted light
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2. Rotate the dichroscope (not the gem) while observing
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3. Look for colour differences between the two images
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4. Rotate the gem to find the direction of maximum colour difference
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5. Record both colours seen
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- title: Tips for Best Results
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content: |
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- Use a strong, white light source
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- View through the body of the stone, not the surface
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- Check multiple directions (rotate the gem 90°)
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- Compare colours side by side in the two windows
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- Work with good eye relief (don't press against eyepiece)
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- title: Interpreting Results
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table:
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headers:
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- Observation
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- Interpretation
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- Example Gems
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rows:
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- ["Two identical colours", "Isotropic or viewing down optic axis", "Spinel, garnet, glass"]
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- ["Two different colours (dichroism)", "Uniaxial gem (trigonal, tetragonal, hexagonal)", "Ruby, sapphire, tourmaline"]
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- ["Three colours visible (trichroism)", "Biaxial gem (orthorhombic, monoclinic, triclinic)", "Tanzanite, alexandrite, iolite"]
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- ["No colour visible", "Colourless or very pale stone", "Colourless topaz, pale beryl"]
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- title: Pleochroism Strength
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content: |
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Pleochroism varies from very weak to very strong:
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subsections:
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- title: Strength Scale
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content: |
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- **None**: Isotropic materials (no pleochroism)
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- **Weak**: Slight colour variation, difficult to see
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- **Distinct**: Clear difference but moderate
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- **Strong**: Obvious colour difference
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- **Very strong**: Dramatic colour change between directions
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- title: Factors Affecting Visibility
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content: |
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- **Colour saturation**: Pale stones show less pleochroism
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- **Viewing direction**: Maximum difference perpendicular to optic axis
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- **Light quality**: Strong, white light shows colours best
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- **Stone size**: Larger stones show colours more clearly
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- title: Diagnostic Pleochroism
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table:
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caption: Characteristic Pleochroism by Gemstone
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headers:
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- Gemstone
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- Strength
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- Colours
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rows:
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- ["Ruby", "Strong", "Purple-red / orange-red"]
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- ["Blue sapphire", "Strong", "Violet-blue / greenish-blue"]
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- ["Emerald", "Distinct", "Blue-green / yellow-green"]
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- ["Tanzanite", "Strong (trichroic)", "Blue / purple / brown"]
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- ["Tourmaline", "Strong", "Variable, often dark / light of same hue"]
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- ["Alexandrite", "Strong (trichroic)", "Green / orange / purple-red"]
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- ["Kunzite", "Strong", "Pink / colourless"]
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- ["Iolite", "Very strong (trichroic)", "Violet / blue / pale yellow"]
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- ["Peridot", "Weak", "Yellow-green / green"]
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- ["Aquamarine", "Weak", "Colourless / pale blue"]
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- ["Andalusite", "Strong (trichroic)", "Yellow-green / brown / red"]
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- ["Hiddenite", "Distinct", "Yellow-green / blue-green"]
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- ["Zircon (blue)", "Weak", "Blue / colourless"]
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- title: Dichroism vs Trichroism
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content: |
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Understanding the distinction:
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subsections:
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- title: Dichroic Gems (Uniaxial)
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content: |
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Uniaxial crystals have two principal optical directions and show
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two pleochroic colours. These belong to:
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- Trigonal system (corundum, tourmaline, quartz)
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- Tetragonal system (zircon, scapolite)
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- Hexagonal system (beryl, apatite)
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- title: Trichroic Gems (Biaxial)
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content: |
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Biaxial crystals have three principal optical directions and can
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show three distinct pleochroic colours. These belong to:
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- Orthorhombic system (topaz, peridot, tanzanite)
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- Monoclinic system (kunzite, diopside)
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- Triclinic system (kyanite)
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To see all three colours, rotate the gem to view along different axes.
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- title: Practical Applications
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callout:
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type: tip
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title: When Pleochroism Matters
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text: |
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The dichroscope is particularly useful for:
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- **Separating ruby from garnet**: Ruby shows strong pleochroism; garnet shows none
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- **Confirming corundum identity**: Characteristic pleochroic colours
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- **Identifying iolite**: Very strong trichroism is diagnostic
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- **Detecting synthetics**: Some synthetics show atypical pleochroism
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- **Assessing cutting orientation**: Colour face-up depends on cut direction
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- title: Common Mistakes
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content: |
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Avoid these errors when using the dichroscope:
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- **Rotating the gem instead of the dichroscope** initially
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- **Using reflected light** instead of transmitted light
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- **Not checking multiple directions** in the stone
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- **Confusing colour zoning** with pleochroism
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- **Testing opaque or heavily included stones** (no light transmission)

‎docs/learn/equipment/index.yaml‎

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title: Gem Testing Equipment Overview
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description: Introduction to gemmological instruments, testing workflow, and which tool to use for different identification tasks.
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order: 1
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category: equipment
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difficulty: beginner
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icon: microscope
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related:
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- refractometer
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- polariscope
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- dichroscope
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- spectroscope
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- microscope
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- uv-lamp
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tags:
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- equipment
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- identification
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- workflow
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- testing
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sections:
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- title: Introduction
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content: |
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Gemmological testing relies on a suite of standard instruments that measure optical and
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physical properties. Mastering these tools is fundamental to gem identification and
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forms the core practical skills tested in the FGA Foundation examination.
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A systematic approach using multiple instruments provides the most reliable identification.
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No single test is definitive—results should be correlated across several methods.
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- title: The Gemmological Toolkit
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content: |
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A well-equipped gemmological laboratory includes the following core instruments:
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subsections:
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- title: Essential Instruments
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table:
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headers:
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- Instrument
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- Primary Function
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- Difficulty
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rows:
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- ["Refractometer", "Measure refractive index and birefringence", "Moderate"]
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- ["Polariscope", "Determine optic character (SR/DR)", "Easy"]
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- ["Dichroscope", "Observe pleochroism in coloured stones", "Easy"]
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- ["Spectroscope", "View absorption spectrum", "Moderate"]
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- ["UV Lamp", "Observe fluorescence reactions", "Easy"]
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- ["Microscope", "Examine inclusions and features", "Moderate"]
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- ["Chelsea Filter", "Quick screening for emeralds", "Easy"]
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- title: Supporting Equipment
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content: |
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Beyond the core instruments, a complete toolkit includes:
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- **Specific gravity balance**: For density measurement
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- **Thermal conductivity probe**: Diamond screening
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- **Loupe (10×)**: Field examination standard
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- **Tweezers and stone holders**: Safe manipulation
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- **Cleaning supplies**: Cloth, brushes, solvents
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- **Reference materials**: Master stones, comparison samples
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- title: Instrument Selection Guide
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table:
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caption: Which Instrument to Use
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headers:
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- Question
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- Primary Instrument
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- Supporting Tests
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rows:
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- ["What is the RI?", "Refractometer", "SG measurement"]
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- ["Is it isotropic or anisotropic?", "Polariscope", "Refractometer (two readings?)"]
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- ["What causes the colour?", "Spectroscope", "Dichroscope, Chelsea filter"]
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- ["Is it natural or synthetic?", "Microscope", "UV lamp, spectroscope"]
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- ["Is it treated?", "Microscope", "UV lamp, spectroscope"]
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- ["What is the origin?", "Microscope", "Spectroscope, chemistry"]
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- title: Testing Workflow
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callout:
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type: tip
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title: Systematic Testing Approach
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text: |
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For unknown gems, follow this sequence:
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1. **Visual examination**: Colour, transparency, lustre, cut style
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2. **Refractometer**: RI and birefringence
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3. **Polariscope**: Optic character (SR/DR)
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4. **Dichroscope**: Pleochroism (if coloured and DR)
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5. **Microscope**: Inclusions, growth features
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6. **Spectroscope**: Absorption spectrum
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7. **UV lamp**: Fluorescence reactions
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8. **Chelsea filter**: If green stone
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9. **SG**: If refractometer inconclusive or OTL
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Document all results before reaching a conclusion.
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- title: High-RI Stones
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callout:
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type: warning
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title: Stones Above Refractometer Limits
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text: |
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Stones with RI above 1.81 cannot be measured on standard refractometers:
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- **Diamond** (RI 2.417) - Use thermal probe or specific gravity
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- **Zircon** (RI 1.93–1.98) - May show partial reading
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- **Demantoid** (RI 1.88) - SG and spectrum for identification
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- **Sphene** (RI 1.90–2.02) - Identify by high dispersion and birefringence
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- title: Recording and Documentation
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content: |
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Accurate documentation is essential for professional practice:
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subsections:
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- title: What to Record
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content: |
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For each stone examined, document:
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- **Date and reference number**
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- **Description**: Weight, dimensions, cut style, colour
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- **All test results**: RI, optic character, pleochroism, spectrum, fluorescence
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- **Inclusions observed**: With photomicrographs if possible
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- **Conclusion**: Identification with confidence level
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- title: Professional Standards
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content: |
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Follow these documentation principles:
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- Record observations objectively, without interpretation bias
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- Note any limitations or uncertainties
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- Keep equipment calibration records
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- Maintain chain of custody for valuable items
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- Store records securely with appropriate confidentiality

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