Quick Reference¶
Rapid lookup tables for common gemmological data.
Refractive Index Table¶
Common gem RI values for refractometer identification:
| Gem | RI | Character |
|---|---|---|
| Diamond | 2.417 | Isotropic |
| Ruby/Sapphire | 1.762-1.770 | Uniaxial (-) |
| Emerald | 1.577-1.583 | Uniaxial (-) |
| Aquamarine | 1.577-1.583 | Uniaxial (-) |
| Spinel | 1.718 | Isotropic |
| Garnet (Pyrope) | 1.746 | Isotropic |
| Garnet (Almandine) | 1.79 | Isotropic |
| Topaz | 1.629-1.637 | Biaxial (+) |
| Tourmaline | 1.624-1.644 | Uniaxial (-) |
| Peridot | 1.654-1.690 | Biaxial (+/-) |
| Quartz | 1.544-1.553 | Uniaxial (+) |
| Zircon (high) | 1.925-1.984 | Uniaxial (+) |
Specific Gravity Table¶
Hydrostatic weighing reference values:
| Gem | SG |
|---|---|
| Diamond | 3.52 |
| Ruby/Sapphire | 4.00 |
| Emerald | 2.72 |
| Spinel | 3.60 |
| Garnet (Pyrope) | 3.78 |
| Topaz | 3.53 |
| Tourmaline | 3.06 |
| Peridot | 3.34 |
| Quartz | 2.65 |
| Zircon | 4.70 |
Hardness Comparison¶
Mohs scale with common gem examples:
| Hardness | Reference Mineral | Gem Examples |
|---|---|---|
| 10 | Diamond | Diamond |
| 9 | Corundum | Ruby, Sapphire |
| 8 | Topaz | Topaz, Spinel |
| 7 | Quartz | Quartz, Tourmaline |
| 6.5-7 | - | Garnet, Peridot |
| 6 | Feldspar | Moonstone, Labradorite |
| 5-6 | - | Opal, Turquoise |
| 4-5 | Fluorite/Apatite | Fluorite |
| 3 | Calcite | Pearl, Coral |
| 2 | Gypsum | Amber |
| 1 | Talc | - |
Crystal Systems¶
Quick reference for the 7 crystal systems:
| System | Axes | Angles | Example Gems |
|---|---|---|---|
| Cubic | a=b=c | 90°/90°/90° | Diamond, Garnet, Spinel |
| Tetragonal | a=b≠c | 90°/90°/90° | Zircon |
| Hexagonal | a=b≠c | 90°/90°/120° | Beryl, Apatite |
| Trigonal | a=b≠c | 90°/90°/120° | Quartz, Ruby, Tourmaline |
| Orthorhombic | a≠b≠c | 90°/90°/90° | Topaz, Peridot |
| Monoclinic | a≠b≠c | 90°/β/90° | Kunzite, Jade |
| Triclinic | a≠b≠c | α/β/γ | Turquoise, Kyanite |
Absorption Spectra¶
Key absorption features for identification:
| Gem | Key Absorptions |
|---|---|
| Ruby | 694 nm (Cr fluorescent line), 659/668 nm doublet |
| Blue Sapphire | 450 nm (Fe²⁺/Fe³⁺), weak 471 nm |
| Emerald | 683/680 nm doublet (Cr), broad absorption in red |
| Almandine Garnet | 504/520/573 nm bands |
| Peridot | Three bands at 453/477/497 nm |
| Zircon | Multiple fine lines (uranium spectrum) |
Chelsea Filter Reactions¶
Red and green stone differentiation:
| Gem | Reaction |
|---|---|
| Emerald (natural) | Red |
| Emerald (synthetic) | Strong red |
| Chrome tourmaline | Red |
| Green tourmaline | Green |
| Tsavorite | Inert/slightly pink |
| Demantoid | Inert |
| Blue cobalt glass | Red |
| Blue spinel (natural) | Inert |
| Blue cobalt spinel | Red |
Fluorescence Guide¶
Common fluorescence reactions under UV:
| Gem | LW UV | SW UV |
|---|---|---|
| Diamond (Cape) | Blue | Blue (weaker) |
| Ruby | Red | Red (weaker) |
| Synthetic ruby | Red (strong) | Red (very strong) |
| Emerald | Usually inert | Usually inert |
| Kunzite | Orange | Orange (strong) |
| Opal | Variable | Variable |
| Pearl (natural) | Weak blue | - |
| Pearl (cultured) | Yellow/green | - |