feat(learn): enrich YAML with Gem-A Diploma transcript data (D2-D7)

Add 9 authoritative knowledge gaps from Gem-A Diploma transcripts:

- Sturman's 7 refractometer patterns (D6 pp.28-29)
- 38-material optical properties table replacing 7-row table (D6 pp.31-32)
- Diagnostic absorption spectra with wavelengths for 8 materials (D7 pp.34-35)
- Streak test data for 7 materials (D4 p.16)
- Band gap theory and physical optics colour mechanisms (D7 pp.27-31)
- Epigenetic inclusions temporal classification (D2)
- Expanded differential hardness and parting sections (D4 pp.14-17)
- Immersion fluids table expanded to 6 entries (D2 p.21)
- Heavy liquids SG testing detail with bromoform (D5)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Bissbert

docs/learn/equipment/microscope.yaml

@@ -142,10 +142,12 @@ sections:
             - Best For
             - Safety Notes
           rows:
-            - ["Water", "1.33", "Basic immersion; safe for all gems", "Safe"]
-            - ["Benzyl benzoate", "1.57", "Quartz, beryl, feldspar", "Low toxicity"]
-            - ["Methylene iodide", "1.74", "Corundum, spinel, garnet", "Toxic; handle with care"]
+            - ["Distilled water", "1.33", "Basic immersion; safe for all gems", "Safe"]
+            - ["Liquid paraffin (also almond oil and baby oil)", "1.47", "General purpose; low-RI materials", "Safe; readily available"]
             - ["Clove oil", "1.54", "General purpose", "Pleasant odour; low toxicity"]
+            - ["Benzyl benzoate", "1.57", "Quartz, beryl, feldspar", "Low toxicity"]
+            - ["1-bromonaphthalene (monobromonaphthalene)", "1.66", "Tourmaline, spodumene, diopside", "Lab use only; avoid skin contact"]
+            - ["Di-iodomethane (methylene iodide)", "1.74", "Corundum, spinel, garnet", "Toxic; handle with care; store in dark bottles"]
 
       - title: Immersion Observations
         content: |

docs/learn/equipment/refractometer.yaml

@@ -97,6 +97,77 @@ sections:
           - Cannot measure birefringence accurately
           - Best for isotropic materials or quick screening
 
+  - title: "Sturman's Seven Refractometer Patterns"
+    content: |
+      Darko Sturman refined the technique of observing shadow-edge behaviour on the
+      refractometer into seven basic patterns that cover all possible observations for
+      isotropic and anisotropic gemstones. Identification of a pattern is based on
+      observations during rotation of a gemstone on the refractometer. Note:
+
+      - The number of shadow edges observed (one or two)
+      - Whether each shadow edge is variable or constant
+      - Whether the shadow edges meet (touch)
+    table:
+      caption: "Sturman's Seven Refractometer Patterns"
+      headers:
+        - Pattern
+        - Shadow Edges
+        - Behaviour
+        - Conclusion
+      rows:
+        - ["I", "1 constant", "RI stays constant during rotation", "Isotropic"]
+        - ["II", "2 constant, parallel", "Neither moves; both at fixed RI values", "Uniaxial (c-axis perpendicular to table)"]
+        - ["III", "2, one constant + one variable, touching", "Edges join to a single edge at one rotation position", "Uniaxial (c-axis parallel to table); sign determinable"]
+        - ["IV", "2, one constant + one variable, not touching", "Higher RI edge moves; edges do not meet", "Uniaxial or biaxial (c-axis oblique if uniaxial)"]
+        - ["V", "2, one constant + one variable, intersecting", "Shadow edges cross each other", "Biaxial"]
+        - ["VI", "2 variable, not touching", "Both move; they do not touch", "Biaxial"]
+        - ["VII", "2 variable, touching", "Both move and touch at one point", "Biaxial; sign determinable"]
+    subsections:
+      - title: "Patterns I-III: Isotropic and Uniaxial"
+        content: |
+          **Pattern I** — A single constant shadow edge confirms the material is isotropic.
+          Ensure the reading stays truly constant during a full rotation.
+
+          **Pattern II** — Two constant, parallel shadow edges that never move. This occurs when
+          the c-axis is perpendicular to the table facet. The minimum and maximum RI and
+          birefringence can be determined, but the optic sign cannot without testing on
+          an alternative facet.
+
+          **Pattern III** — One constant and one variable edge that join together at one point
+          during rotation. This confirms uniaxial character with the c-axis parallel to the
+          table. The optic sign is determinable:
+
+          - If omega < epsilon (constant < variable): **uniaxial positive**
+          - If omega > epsilon (constant > variable): **uniaxial negative**
+
+      - title: "Patterns IV-VII: Biaxial Determination"
+        content: |
+          **Pattern IV** — One constant edge, one variable edge, not touching. This ambiguous
+          pattern can occur in both uniaxial (oblique c-axis) and biaxial stones.
+
+          **Pattern V** — Shadow edges intersect (cross each other). This confirms biaxial
+          character. The edges may both converge towards beta.
+
+          **Pattern VI** — Both edges move but do not touch. Confirms biaxial, but the optic
+          sign cannot be determined without additional information.
+
+          **Pattern VII** — Both edges move and touch at one point. Confirms biaxial with
+          determinable optic sign.
+
+      - title: Optic Sign Determination
+        content: |
+          **Uniaxial optic sign** (Pattern III):
+
+          - omega < epsilon → positive
+          - omega > epsilon → negative
+
+          **Biaxial optic sign** (when both edges move):
+
+          - Observe which shadow edge crosses the point halfway between the maximum
+            (gamma) and minimum (alpha) values — this edge gives beta
+          - Beta closer to alpha → **biaxial positive**
+          - Beta closer to gamma → **biaxial negative**
+
   - title: Troubleshooting
     content: |
       Common problems and solutions when using the refractometer:

docs/learn/fundamentals/chemical-properties.yaml

@@ -202,6 +202,29 @@ sections:
 
           Understanding stability is important for predicting colour permanence.
 
+  - title: Diagnostic Absorption Spectra
+    content: |
+      The spectroscope can identify materials by their characteristic absorption patterns.
+      Not all coloured materials have recognizable spectra, and some colourless materials
+      (zircon, diamond, jadeite) may still show diagnostic absorption. The following are
+      the most diagnostically useful spectra from the Gem-A Diploma course.
+    table:
+      caption: Key Diagnostic Absorption Spectra
+      headers:
+        - Material
+        - Chromophore
+        - Key Wavelengths
+        - Diagnostic Notes
+      rows:
+        - ["Chrysoberyl", "Fe", "Band centred at 444 nm", "Distinguishes yellow/greenish/brown chrysoberyl from sapphire; useful for cat's eyes in settings"]
+        - ["Alexandrite", "Cr", "Lines in red; broad band in yellow-green", "Pleochroic variation visible — spectrum shifts between daylight and tungsten light"]
+        - ["Synthetic colour-change sapphire", "V + Cr", "Sharp fine line at 475 nm", "Diagnostic for vanadium in corundum; line may be faint"]
+        - ["Jadeite (pale specimens)", "Fe", "Fine line at 437 nm", "Seen in pale specimens of various colours; green stones may also show Cr lines in red"]
+        - ["Dyed jadeite", "Fe + Cr-dye", "Weak band(s) in red + 437 nm line", "Chromium-green dye gives additional band(s) in red; diagnostic for dye detection"]
+        - ["Diamond (Cape yellow)", "N", "Fine line at 415 nm", "Most prominent of several fine lines; easier to see when diamond is cooled (liquid nitrogen or dry ice)"]
+        - ["Apatite", "REE", "Multiple fine-line bands in yellow-green", "'Didymium' or rare earth spectrum; each band consists of many fine lines ending in a sharp edge"]
+        - ["Pink YAG", "REE", "Cluster of lines/bands in yellow-orange", "Example of REE-doped artificial material; CZ and glass may show similar spectra"]
+
   - title: Chemical Formulas Reference
     content: |
       Chemical formulas help understand gem composition and elemental substitutions.
@@ -251,6 +274,108 @@ sections:
             - ["Amazonite", "Microcline", "KAlSi₃O₈"]
             - ["Sunstone", "Oligoclase", "(Na,Ca)(Al,Si)₄O₈"]
 
+  - title: Band Gap Theory
+    content: |
+      All gem materials are held together by electronic bonding. In some materials,
+      electrons can move throughout the crystal structure at a higher energy level than
+      those bound within atomic orbitals. The gap between the atom-bound "valence band"
+      electrons and the wandering "conduction band" electrons is the electron energy band
+      gap — a "forbidden" zone whose width greatly influences optical properties.
+    subsections:
+      - title: Three Material Types
+        content: |
+          Materials having a band gap can be grouped into three types:
+
+          1. **Large band gap** (wider than visible light range): Even violet light cannot
+             excite electrons across the gap. No visible light is absorbed, so the material
+             appears transparent and colourless when pure. Most gemstones fall into this
+             category — pure diamond, corundum, quartz, and topaz.
+
+          2. **Small band gap** (narrower than red light energy): All visible light interacts
+             with electrons and is absorbed, making the material opaque.
+
+          3. **Overlapping band gap**: The gap energy partially overlaps the visible spectrum,
+             causing selective absorption and a residual colour.
+
+      - title: Diamond Band Gap Colour
+        content: |
+          Diamond provides the key example of band gap colour through impurity energy levels:
+
+          **Nitrogen (yellow)**: Carbon has four valence electrons; nitrogen has five. When
+          nitrogen replaces a carbon atom, the extra electron creates a donor level within the
+          band gap. Excitation of this electron absorbs light from the middle of the visible
+          spectrum through blue and violet, producing a pronounced yellow ("canary") colour.
+          This is distinct from the "Cape" yellow caused by nitrogen vacancy colour centres.
+
+          **Boron (blue)**: Boron has only three valence electrons, creating an acceptor level
+          near the top of the valence band. Absorption occurs at maximum in the near infrared,
+          extending into lower-energy visible light. Higher-energy blue and violet light is
+          transmitted, producing blue colour. Because the boron level is close to the valence
+          band, electrons can be thermally excited at room temperature, leaving "holes" that
+          allow electrical current — boron-containing diamonds conduct electricity.
+
+  - title: Physical Optics Colour
+    content: |
+      Not all colour in gemstones results from absorption of light by electronic mechanisms.
+      Physical phenomena can also produce colour through the interaction of light with
+      structures within or on the surface of a material.
+    subsections:
+      - title: Dispersion
+        content: |
+          Dispersion separates white light into its component colours ("fire"). The degree
+          of dispersion depends on the refractive index variation across wavelengths. Diamond's
+          high dispersion (0.044) produces the spectral flashes characteristic of a well-cut
+          brilliant.
+
+      - title: Diffraction
+        content: |
+          The play-of-colour in precious opal is caused by diffraction of light by regularly
+          stacked three-dimensional groups of silica spheres. These spheres are only a few
+          hundred nanometres in diameter, with gaps of similar size to visible light wavelengths.
+
+          The actual colours seen depend on the size of the spheres:
+          - Large spheres: full range of colours from violet to red (most desirable)
+          - Medium spheres: violet to green only
+          - Small spheres: only violet and blue light can pass between them
+
+      - title: Thin-Film Interference
+        content: |
+          Thin-film interference colour arises from closely-spaced double reflections from
+          thin films, layers of differing composition, or thin-film cavities such as cracks.
+          When two reflected rays travel in the same direction and their wave peaks coincide
+          ("in phase"), they reinforce each other. When peak meets trough ("out of phase"),
+          they cancel — this is interference.
+
+          Examples in gemmology:
+          - **Labradorite**: iridescent colours from interference at thin compositional layers
+          - **Pearl nacre**: lustre from diffraction at overlapping platy aragonite crystals
+            combined with interference from thin nacre layers
+          - **Crack iridescence**: colours from thin films of air in cracks (as in topaz,
+            glass, or quartz) — similar to oil films on water
+
+      - title: Scattering
+        content: |
+          Scattering occurs when light is randomly reflected by particles within a substance.
+          Blue light is typically much more strongly scattered than red.
+
+          The scattering effect is most noticeable when particles are smaller than approximately
+          400 nm in size. This causes the blue adularescence (sheen) in fine-quality moonstone,
+          where scattering is caused by submicroscopic particles of albite feldspar.
+
+          As particles get larger, other colours such as red and green may be seen at certain
+          angles. Larger particles still produce a whitish effect called opalescence — seen in
+          materials such as common opal and milky quartz. This should not be confused with the
+          play-of-colour effect in precious opal.
+
+      - title: Inclusions
+        content: |
+          Fine needle-like inclusions can interact with light to produce optical phenomena:
+
+          - **Chatoyancy** (cat's eye effect): caused by scattering of light from parallel
+            needle-like inclusions
+          - **Asterism** (star effect): caused by multiple sets of oriented needle-like
+            inclusions (typically rutile silk in corundum)
+
   - title: Trace Element Effects
     content: |
       Minor and trace elements significantly affect gem properties beyond colour.

docs/learn/fundamentals/optical-properties.yaml

@@ -31,19 +31,51 @@ sections:
       1.35 to 1.81 (limited by the contact liquid). Gems with higher RI require
       alternative methods.
     table:
-      caption: RI Values by Gemstone
+      caption: Optical Properties of Common Gem Materials
       headers:
-        - Gemstone
-        - RI Range
-        - Optic Character
+        - Material
+        - RI
+        - Birefringence
+        - Optical Character
       rows:
-        - ["Diamond", "2.417", "Isotropic"]
-        - ["Corundum", "1.762-1.770", "Uniaxial -"]
-        - ["Spinel", "1.712-1.736", "Isotropic"]
-        - ["Tourmaline", "1.624-1.644", "Uniaxial -"]
-        - ["Topaz", "1.609-1.617", "Biaxial +"]
-        - ["Quartz", "1.544-1.553", "Uniaxial +"]
-        - ["Beryl", "1.570-1.590", "Uniaxial -"]
+        - ["Amber", "1.54 approx.", "-", "I"]
+        - ["Andalusite", "1.63-1.64", "0.007-0.013", "B-"]
+        - ["Apatite", "1.63-1.64", "0.002-0.006", "U-"]
+        - ["Beryl varieties", "1.56-1.60", "0.003-0.010", "U-"]
+        - ["Calcite varieties", "1.48-1.66", "0.172", "U-"]
+        - ["Chrysoberyl", "1.74-1.76", "0.008-0.010", "B+"]
+        - ["Corundum varieties", "1.76-1.78", "0.008-0.009", "U-"]
+        - ["Cubic zirconia", "2.17 approx.", "-", "I"]
+        - ["Diamond", "2.42", "-", "I"]
+        - ["Diopside", "1.67-1.70", "0.024-0.030", "B+"]
+        - ["Feldspar varieties", "1.52-1.57", "0.004-0.009", "B+/-"]
+        - ["Fluorite", "1.43-1.44", "-", "I"]
+        - ["Garnet, almandine", "1.76-1.81", "-", "I"]
+        - ["Garnet, demantoid", "1.89 approx.", "-", "I"]
+        - ["Garnet, grossular", "1.73-1.75", "-", "I"]
+        - ["Garnet, hydrogrossular", "1.70-1.73", "-", "I"]
+        - ["Garnet, pyrope", "1.74-1.76", "-", "I"]
+        - ["Garnet, spessartine", "1.79-1.82", "-", "I"]
+        - ["Iolite", "1.54-1.56", "0.008-0.012", "B-"]
+        - ["Natural glass", "1.50 approx.", "-", "I"]
+        - ["Opal", "1.40-1.46", "-", "I"]
+        - ["Paste (artificial glass)", "1.50-1.70", "-", "I"]
+        - ["Peridot", "1.65-1.69", "0.036", "B+/-"]
+        - ["Quartz, crystalline", "1.54-1.56", "0.009", "U+"]
+        - ["Quartz, polycrystalline", "1.53-1.55", "-", "-"]
+        - ["Rhodochrosite", "1.59-1.82", "0.220", "U-"]
+        - ["Scapolite", "1.54-1.58", "0.009-0.026", "U-"]
+        - ["Sinhalite", "1.67-1.71", "0.037-0.038", "B-"]
+        - ["Sphene", "1.88-2.05", "0.105-0.135", "B+"]
+        - ["Spinel", "1.71-1.74", "-", "I"]
+        - ["Spinel, Verneuil synthetic", "1.72-1.73", "-", "I"]
+        - ["Spodumene", "1.66-1.68", "0.015-0.016", "B+"]
+        - ["Synthetic moissanite", "2.65-2.69", "0.043", "U"]
+        - ["Tanzanite", "1.69-1.70", "0.006-0.013", "B+"]
+        - ["Topaz", "1.61-1.64", "0.008-0.010", "B+"]
+        - ["Tourmaline", "1.62-1.65", "0.014-0.021", "U-"]
+        - ["YAG", "1.83 approx.", "-", "I"]
+        - ["Zircon", "1.78-1.99", "up to 0.059", "U+"]
 
   - title: Birefringence
     content: |