Pleochroism of Gemstones — Dichroscope Reference Chart
Last updated: August 2026
Pleochroism strength and observed pleochroic colors for 132 gemstone species, sorted strongest first. 34 species show strong dichroism or trichroism — readable in seconds with a calcite dichroscope.
Common pleochroism lookups: Tanzanite strong trichroic · Iolite strong trichroic · Andalusite strong trichroic · Alexandrite strong trichroic · Kunzite strong trichroic · Tourmaline strong dichroic · Sapphire strong dichroic · Ruby strong dichroic
Pleochroism is the property of a doubly refractive gemstone showing different body colors in different crystal directions, because its two (or three) polarized rays are absorbed differently. The instrument for observing it is the dichroscope — a small tube containing a calcite rhomb or polarizing filters that shows the two rays side by side. Rotate the stone under strong light and compare the twin windows: two distinct colors means the stone is dichroic; three colors found across different directions means trichroic.
Pleochroism is fast, needs no contact fluid, and works on mounted stones — which makes it a favorite opening test. A strongly pleochroic reading immediately proves the stone is doubly refractive, ruling out glass, spinel, garnet, and diamond. It also separates classic look-alikes: iolite (violet-blue, light blue, yellow-gray) is famously "dichroite" for its dramatic three-color display, and tanzanite shows blue, violet, burgundy — while a blue sapphire shows only its two blues.
Absence of pleochroism is evidence too, but read it carefully: singly refractive and aggregate stones show none — apart from the metamict case in the FAQ below, and even strongly dichroic species show little when viewed straight down the optic axis. Always check several directions before recording "none." The colors listed below are the pleochroic colors recorded for each species in the Loupewise engine; strength is graded none, weak, moderate, strong dichroic, or strong trichroic.
Studying for the GIA or FGA practical? Loupewise drills dichroscope observations alongside RI and optic character and runs timed mock exams built around the real exam formats.
Practice exams →| Gem | Pleochroism | Pleochroic Colors | Optic Character |
|---|---|---|---|
| Alexandrite | Strong Trichroic | Green, Orange, Purple-red | Biaxial (+) |
| Andalusite | Strong Trichroic | Green, Red-brown, Yellow-orange | Biaxial (−) |
| Chrysoberyl | Strong Trichroic | Colorless, Yellow, Green | Biaxial (+) |
| Diaspore | Strong Trichroic | Colorless, Pale yellow-green, Pink-champagne | Biaxial (+) |
| Enstatite | Strong Trichroic | Green, Yellow-green, Brown-green | Biaxial (+) |
| Grandidierite | Strong Trichroic | Dark blue-green, Colorless, Dark green | Biaxial (−) |
| Hiddenite | Strong Trichroic | Colorless, Yellow-green, Emerald green | Biaxial (+) |
| Iolite | Strong Trichroic | Violet-blue, Light blue, Yellow-gray | Biaxial (−) |
| Kornerupine | Strong Trichroic | Colorless, Brown-yellow, Green | Biaxial (−) |
| Kunzite | Strong Trichroic | Pink, Violet, Colorless | Biaxial (+) |
| Kyanite | Strong Trichroic | Colorless, Dark blue, Violet-blue | Biaxial (−) |
| Sinhalite | Strong Trichroic | Pale brown, Dark brown, Greenish-brown | Biaxial (−) |
| Sphene | Strong Trichroic | Colorless, Yellow-green, Reddish-brown | Biaxial (+) |
| Tanzanite | Strong Trichroic | Blue, Violet, Burgundy | Biaxial (+) |
| Cassiterite | Strong Dichroic | Yellow-brown, Red-brown | Uniaxial (+) |
| Chrome Tourmaline | Strong Dichroic | Dark green, Brownish-green | Uniaxial (−) |
| Cinnabar | Strong Dichroic | Red, Brownish red | Uniaxial (+) |
| Color-Change Sapphire | Strong Dichroic | Blue-green, Purple-violet | Uniaxial (−) |
| Emerald | Strong Dichroic | Bluish-green, Yellowish-green | Uniaxial (−) |
| Green Tourmaline | Strong Dichroic | Dark green, Yellowish-green | Uniaxial (−) |
| Indicolite | Strong Dichroic | Dark blue, Light blue | Uniaxial (−) |
| Padparadscha Sapphire | Strong Dichroic | Orangey-pink, Pale orange-yellow | Uniaxial (−) |
| Paraiba Tourmaline | Strong Dichroic | Dark blue-green, Light blue | Uniaxial (−) |
| Pink Sapphire | Strong Dichroic | Pink, Orange-pink | Uniaxial (−) |
| Red Beryl | Strong Dichroic | Red, Orange-red | Uniaxial (−) |
| Rubellite | Strong Dichroic | Dark red, Pale pink | Uniaxial (−) |
| Ruby | Strong Dichroic | Purplish-red, Orangey-red | Uniaxial (−) |
| Sapphire | Strong Dichroic | Violet-blue, Greenish-blue | Uniaxial (−) |
| Scapolite | Strong Dichroic | Colorless, Violet | Uniaxial (−) |
| Star Ruby | Strong Dichroic | Purplish-red, Orangey-red | Uniaxial (−) |
| Star Sapphire | Strong Dichroic | Violet-blue, Greenish-blue | Uniaxial (−) |
| Synthetic Color-Change Corundum | Strong Dichroic | Purple-blue, Purple-red | Uniaxial (−) |
| Tourmaline | Strong Dichroic | Depth of tint; no fixed pair | Uniaxial (−) |
| Watermelon Tourmaline | Strong Dichroic | Pink, Green | Uniaxial (−) |
| Apatite | Moderate | Colorless, Blue | Uniaxial (−) |
| Benitoite | Moderate | Blue, Colorless | Uniaxial (+) |
| Chrome Diopside | Moderate | Bluish-green, Yellowish-green | Biaxial (+) |
| Morganite | Moderate | Pale pink, Deeper bluish-pink | Uniaxial (−) |
| Topaz | Moderate | Colorless, Pale blue, Pink | Biaxial (+) |
| Zircon | Moderate | Blue, Colorless | Uniaxial (+) |
| Amazonite | Weak | — | Biaxial (−) |
| Amethyst | Weak | Purplish-red, Bluish-purple | Uniaxial (+) |
| Ametrine | Weak | Pale purple, Pale yellow | Uniaxial (+) |
| Aquamarine | Weak | Colorless, Light blue | Uniaxial (−) |
| Calcite | Weak | — | Uniaxial (−) |
| Cat's Eye Chrysoberyl | Weak | Colorless, Yellow, Green | Biaxial (+) |
| Citrine | Weak | Light yellow, Deep yellow | Uniaxial (+) |
| Clinohumite | Weak | Yellow, Pale yellow, Orange-yellow | Biaxial (+) |
| Heliodor | Weak | Pale yellow, Greenish-yellow | Uniaxial (−) |
| Labradorite | Weak | Yellow, Blue, Green | Biaxial (+) |
| Low-Type Zircon | Weak | — | SR |
| Moissanite | Weak | Colorless, Pale bluish-green | Uniaxial (+) |
| Peridot | Weak | Yellow-green, Green, Colorless | Biaxial (+) |
| Prasiolite | Weak | Pale green, Colorless | Uniaxial (+) |
| Rainbow Moonstone | Weak | Colorless, Pale yellow | Biaxial (−) |
| Rhodochrosite | Weak | Pink, Pale pink | Uniaxial (−) |
| Rhodonite | Weak | Reddish pink, Yellowish red | Biaxial (+) |
| Rose Quartz | Weak | Pale pink, Deep pink | Uniaxial (+) |
| Smoky Quartz | Weak | Brown, Grayish brown | Uniaxial (+) |
| Sunstone | Weak | Pale yellow, Orange-red, Colorless | Biaxial (−) |
| Taaffeite | Weak | Pink, Colorless | Uniaxial (−) |
| Thulite | Weak | Pink, Pale pink, Colorless | Biaxial (+) |
| White Sapphire | Weak | Colorless, Faint grayish-white | Uniaxial (−) |
| Yellow Sapphire | Weak | Yellow, Pale yellow | Uniaxial (−) |
| Agate | None | — | Aggregate |
| Almandine Garnet | None | — | SR |
| Amber | None | — | SR |
| Aventurine | None | — | Aggregate |
| Black Opal | None | — | SR |
| Black Spinel | None | — | SR |
| Bloodstone | None | — | Aggregate |
| Blue Diamond | None | — | SR |
| Brown Diamond | None | — | SR |
| Carnelian | None | — | Aggregate |
| Chalcedony | None | — | Aggregate |
| Charoite | None | — | Aggregate |
| Chrysocolla | None | — | Aggregate |
| Chrysocolla Chalcedony | None | — | Aggregate |
| Chrysoprase | None | — | Aggregate |
| Color-Change Garnet | None | — | SR |
| Coral | None | — | Aggregate |
| Cubic Zirconia | None | — | SR |
| Cuprite | None | — | SR |
| Danburite | None | — | Biaxial (−) |
| Demantoid Garnet | None | — | SR |
| Diamond | None | — | SR |
| Fire Opal | None | — | SR |
| Fluorite | None | — | SR |
| Goshenite | None | — | Uniaxial (−) |
| Grossular Garnet | None | — | SR |
| Hackmanite | None | — | SR |
| Hauyne | None | — | SR |
| Hawk's Eye | None | — | Aggregate |
| Hematite | None | — | Uniaxial (−) |
| Hessonite Garnet | None | — | SR |
| Howlite | None | — | Aggregate |
| Ivory | None | — | Aggregate |
| Jadeite | None | — | Aggregate |
| Jet | None | — | SR |
| Lapis Lazuli | None | — | Aggregate |
| Larimar | None | — | Biaxial (+) |
| Malachite | None | — | Biaxial (−) |
| Malaya / Umbalite Garnet | None | — | SR |
| Moldavite | None | — | SR |
| Moonstone | None | — | Biaxial (−) |
| Nephrite | None | — | Aggregate |
| Obsidian | None | — | SR |
| Onyx | None | — | Aggregate |
| Opal | None | — | SR |
| Pearl | None | — | Aggregate |
| Phenakite | None | — | Uniaxial (+) |
| Pietersite | None | — | Aggregate |
| Pink Diamond | None | — | SR |
| Prehnite | None | — | Biaxial (+) |
| Pyrope Garnet | None | — | SR |
| Rhodolite Garnet | None | — | SR |
| Rock Crystal | None | — | Uniaxial (+) |
| Serpentine | None | — | Aggregate |
| Sodalite | None | — | Aggregate |
| Spessartite Garnet | None | — | SR |
| Sphalerite | None | — | SR |
| Spinel | None | — | SR |
| Star Diopside | None | — | Biaxial (+) |
| Star Garnet | None | — | SR |
| Sugilite | None | — | Uniaxial (−) |
| Synthetic Spinel | None | — | SR |
| Tiger's Eye | None | — | Aggregate |
| Tsavorite Garnet | None | — | SR |
| Turquoise | None | — | Aggregate |
| Variscite | None | — | Biaxial (−) |
| YAG | None | — | SR |
| Yellow Diamond | None | — | SR |
Click a column header to re-sort the table.
Which gemstones are trichroic?
14 species in this chart are recorded as strongly trichroic: Alexandrite, Andalusite, Chrysoberyl, Diaspore, Enstatite, Grandidierite, Hiddenite, Iolite, Kornerupine, Kunzite, Kyanite, Sinhalite, Sphene, Tanzanite. Trichroism is only possible in biaxial stones — seeing three colors immediately narrows the candidate list.
What is the pleochroism of tanzanite?
Tanzanite is strong trichroic, showing blue, violet, burgundy in its three crystal directions — one of the most dramatic dichroscope displays among blue stones, and a quick separation from blue sapphire.
Can a singly refractive stone show pleochroism?
Almost never, and the exception is worth knowing. Pleochroism needs double refraction — two rays traveling at different speeds and absorbed differently — so a clear pleochroic reaction rules out glass, spinel, garnet, and diamond at once. Low-Type Zircon is the one species in this chart graded pleochroic while still reading singly refractive: it is metamict, meaning internal radiation damage has driven the crystal lattice partway toward amorphous. It stays dark between crossed polars while keeping a very weak residual dichroism (Anderson, Gem Testing). The practical rule: a strong pleochroic reading proves double refraction, a barely-there one does not.
All instrument charts: Refractive Index · Specific Gravity · Mohs Hardness · Birefringence · Fluorescence · Spectroscope · Optic Character · Chelsea & Hanneman Filters · Dispersion · Magnetism
See also: Full Reference Database · How to Identify a Gemstone · Exam Study Guides · Open dataset (CSV & JSON, CC BY 4.0)
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