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feat: Add learn content as structured YAML data
Add FGA curriculum-aligned learn content in YAML format for consumption by gemmology.dev. Content covers: - Crystal systems (7 systems, axes, angles, point groups) - Physical properties (hardness, SG, cleavage, fracture, lustre) - Optical properties (RI, birefringence, pleochroism, dispersion) - Inclusions (diagnostic inclusions, origin determination) - Treatments (heat, filling, diffusion, coating, irradiation) - Synthetics (flame fusion, flux, hydrothermal, CVD/HPHT) Also adds Markdown stub files for MkDocs compatibility. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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‎docs/learn/crystal-systems.md‎

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# Crystal Systems
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The seven crystal systems and their characteristic symmetry elements.
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!!! tip "Interactive Version"
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For interactive crystal visualizations and detailed data tables, visit [gemmology.dev/learn/crystal-systems](https://gemmology.dev/learn/crystal-systems).
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## Overview
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All crystals belong to one of seven crystal systems, classified by their unit cell geometry and symmetry elements. Understanding these systems is fundamental to crystallography and gem identification.
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Crystal systems are defined by the relationship between crystallographic axes (a, b, c) and the angles between them (α, β, γ). Each system has characteristic symmetry elements that determine possible crystal forms.
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## The Seven Systems
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| System | Axes | Angles | Example Gems |
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|--------|------|--------|--------------|
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| Cubic | a = b = c | α = β = γ = 90° | Diamond, Spinel, Garnet |
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| Hexagonal | a₁ = a₂ = a₃ ≠ c | α = β = 90°, γ = 120° | Beryl, Apatite |
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| Trigonal | a₁ = a₂ = a₃ ≠ c | α = β = 90°, γ = 120° | Quartz, Ruby, Tourmaline |
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| Tetragonal | a = b ≠ c | α = β = γ = 90° | Zircon, Rutile |
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| Orthorhombic | a ≠ b ≠ c | α = β = γ = 90° | Topaz, Peridot |
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| Monoclinic | a ≠ b ≠ c | α = γ = 90°, β ≠ 90° | Kunzite, Orthoclase |
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| Triclinic | a ≠ b ≠ c | α ≠ β ≠ γ ≠ 90° | Turquoise, Labradorite |
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## Optic Character
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| System | Optic Character | RI Values |
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|--------|-----------------|-----------|
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| Cubic | Isotropic | Single RI (n) |
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| Hexagonal, Trigonal, Tetragonal | Uniaxial | Two values (ω, ε) |
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| Orthorhombic, Monoclinic, Triclinic | Biaxial | Three values (α, β, γ) |
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---
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*Data source: `learn/crystal-systems.yaml`*

‎docs/learn/crystal-systems.yaml‎

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title: Crystal Systems
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description: The seven crystal systems and their characteristic symmetry elements.
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order: 1
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category: fundamentals
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difficulty: beginner
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icon: cube
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related:
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- physical-properties
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- optical-properties
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tags:
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- crystallography
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- symmetry
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- identification
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sections:
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- title: Overview
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content: |
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All crystals belong to one of seven crystal systems, classified by their unit cell
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geometry and symmetry elements. Understanding these systems is fundamental to
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crystallography and gem identification.
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Crystal systems are defined by the relationship between crystallographic axes
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(a, b, c) and the angles between them (α, β, γ). Each system has characteristic
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symmetry elements that determine possible crystal forms.
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- title: Symmetry Elements
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items:
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- name: Rotation Axes
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description: 2-fold, 3-fold, 4-fold, 6-fold rotational symmetry
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- name: Mirror Planes
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description: Reflection symmetry planes
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- name: Center of Symmetry
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description: Inversion through a point
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- title: The Seven Systems
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subsections:
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- title: Cubic (Isometric)
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content: The highest symmetry system with four threefold axes.
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items:
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- name: Axes
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value: "a = b = c"
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- name: Angles
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value: "α = β = γ = 90°"
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- name: Minimum Symmetry
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value: "4 threefold axes"
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- name: Point Groups
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value: "m3m, 432, -43m, m3, 23"
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- name: Example Gems
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description: Diamond, Spinel, Garnet
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examples:
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- Diamond
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- Spinel
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- Garnet
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- Fluorite
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- title: Hexagonal
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content: Characterized by one sixfold axis.
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items:
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- name: Axes
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value: "a₁ = a₂ = a₃ ≠ c"
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- name: Angles
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value: "α = β = 90°, γ = 120°"
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- name: Minimum Symmetry
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value: "1 sixfold axis"
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- name: Point Groups
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value: "6/mmm, 622, 6mm, -62m, 6/m, 6, -6"
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- name: Example Gems
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description: Beryl, Apatite
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examples:
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- Emerald
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- Aquamarine
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- Morganite
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- Apatite
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- title: Trigonal (Rhombohedral)
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content: Characterized by one threefold axis.
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items:
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- name: Axes
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value: "a₁ = a₂ = a₃ ≠ c"
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- name: Angles
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value: "α = β = 90°, γ = 120°"
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- name: Minimum Symmetry
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value: "1 threefold axis"
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- name: Point Groups
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value: "-3m, 32, 3m, -3, 3"
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- name: Example Gems
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description: Quartz, Corundum, Tourmaline
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examples:
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- Quartz
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- Ruby
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- Sapphire
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- Tourmaline
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- title: Tetragonal
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content: Characterized by one fourfold axis.
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items:
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- name: Axes
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value: "a = b ≠ c"
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- name: Angles
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value: "α = β = γ = 90°"
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- name: Minimum Symmetry
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value: "1 fourfold axis"
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- name: Point Groups
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value: "4/mmm, 422, 4mm, -42m, 4/m, 4, -4"
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- name: Example Gems
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description: Zircon, Rutile
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examples:
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- Zircon
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- Rutile
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- title: Orthorhombic
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content: Three twofold axes or two mirror planes.
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items:
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- name: Axes
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value: "a ≠ b ≠ c"
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- name: Angles
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value: "α = β = γ = 90°"
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- name: Minimum Symmetry
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value: "3 twofold axes or 2 planes"
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- name: Point Groups
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value: "mmm, 222, mm2"
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- name: Example Gems
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description: Topaz, Peridot, Chrysoberyl
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examples:
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- Topaz
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- Peridot
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- Chrysoberyl
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- Tanzanite
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- title: Monoclinic
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content: One twofold axis or one mirror plane.
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items:
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- name: Axes
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value: "a ≠ b ≠ c"
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- name: Angles
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value: "α = γ = 90°, β ≠ 90°"
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- name: Minimum Symmetry
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value: "1 twofold axis or 1 plane"
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- name: Point Groups
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value: "2/m, 2, m"
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- name: Example Gems
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description: Orthoclase, Jadeite, Spodumene
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examples:
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- Kunzite
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- Orthoclase
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- Jadeite
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- title: Triclinic
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content: Lowest symmetry - no rotational symmetry.
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items:
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- name: Axes
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value: "a ≠ b ≠ c"
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- name: Angles
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value: "α ≠ β ≠ γ ≠ 90°"
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- name: Minimum Symmetry
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value: "No rotational symmetry"
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- name: Point Groups
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value: "-1, 1"
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- name: Example Gems
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description: Plagioclase, Rhodonite
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examples:
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- Turquoise
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- Labradorite
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- Rhodonite
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- title: Identifying Crystal Systems
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content: |
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When examining a crystal or gemstone, you can often determine its crystal system
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by observing:
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- **Crystal habit** - The external shape and face arrangement
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- **Optic character** - Isotropic (cubic) vs. uniaxial vs. biaxial
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- **Interference figure** - Under polarized light microscopy
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- **Cleavage directions** - Related to internal symmetry
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- title: Quick Reference
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table:
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caption: Crystal Systems and Optic Character
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headers:
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- System
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- Optic Character
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- RI Values
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rows:
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- ["Cubic", "Isotropic", "Single RI (n)"]
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- ["Hexagonal, Trigonal, Tetragonal", "Uniaxial", "Two RI values (ω, ε)"]
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- ["Orthorhombic, Monoclinic, Triclinic", "Biaxial", "Three RI values (α, β, γ)"]
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- title: Common Gemstones by System
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comparison:
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items:
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- title: Cubic
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points:
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- Diamond
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- Spinel
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- "Garnet (almandine, pyrope, grossular)"
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- Fluorite
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- title: Trigonal
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points:
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- "Quartz (amethyst, citrine)"
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- Ruby
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- Sapphire
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- Tourmaline
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- title: Hexagonal
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points:
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- Emerald
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- Aquamarine
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- Morganite
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- Apatite
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- title: Orthorhombic
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points:
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- Topaz
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- Peridot
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- Chrysoberyl
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- Tanzanite

‎docs/learn/inclusions.md‎

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# Inclusions
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Diagnostic inclusions and fingerprinting techniques for gem identification.
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!!! tip "Interactive Version"
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For detailed data tables and interactive content, visit [gemmology.dev/learn/inclusions](https://gemmology.dev/learn/inclusions).
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## Types of Inclusions
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### Solid Inclusions
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Crystals of other minerals trapped during growth.
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| Host Gem | Common Inclusions |
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|----------|-------------------|
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| Ruby/Sapphire | Rutile silk, zircon halos, calcite |
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| Emerald | Pyrite, calcite, tremolite, mica |
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| Diamond | Garnet, olivine, chromite |
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### Fluid Inclusions
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- **Two-phase** - Liquid + gas bubble
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- **Three-phase** - Liquid + gas + solid crystal (diagnostic for Colombian emerald)
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- **Fingerprint inclusions** - Healed fractures with fluid remnants
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### Growth Features
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- Colour zoning
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- Growth tubes
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- Twinning
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- Phantoms
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## Origin Determination
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### Corundum by Origin
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| Origin | Characteristic Inclusions |
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|--------|---------------------------|
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| Burma (Ruby) | Short rutile silk, calcite, swirl patterns |
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| Kashmir (Sapphire) | Tourmaline, zircon halos, milky zones |
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| Sri Lanka | Long rutile silk, hexagonal colour zoning |
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### Emerald by Origin
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| Origin | Characteristic Inclusions |
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|--------|---------------------------|
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| Colombia | Three-phase inclusions with halite cube |
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| Zambia | Black mica flakes, amphibole needles |
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| Brazil | Biotite mica, pyrite |
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## Natural vs Synthetic
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| Natural Indicators | Synthetic Indicators |
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|--------------------|----------------------|
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| Mineral inclusions | Curved striae |
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| Three-phase inclusions | Gas bubbles |
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| Fingerprint patterns | Flux inclusions |
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| Irregular zoning | Chevron zoning |
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---
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*Data source: `learn/inclusions.yaml`*

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