UV Fluorescence of Gemstones — LW & SW Chart for 130 Gems

Common fluorescence lookups: Ruby LW variable · Diamond LW variable · Amber LW strong blue · Spinel LW variable · Fluorite LW strong blue · Emerald LW variable · Sapphire LW variable · Opal LW variable

UV fluorescence is one of the most underutilized tests in field gemology, yet it is also one of the fastest and requires only an inexpensive UV lamp. When a gemstone is exposed to ultraviolet light, certain trace elements or crystal structure defects cause it to emit visible light — a phenomenon called fluorescence. The color and intensity of that emission varies by species and, critically, can differ between natural and synthetic specimens of the same stone.

Gemologists use two UV wavelengths: longwave UV at approximately 365 nm (LW UV, also called "black light") and shortwave UV at approximately 254 nm (SW UV). The LW response and SW response are often different and both carry diagnostic value. Natural ruby, for example, typically fluoresces strong red under LW UV due to chromium, which also enhances its apparent red color in daylight. Synthetic ruby grown by flame fusion often shows the same strong red, but certain synthetic rubies grown by flux or hydrothermal methods can show different intensities. By contrast, red spinel — a common ruby simulant — shows a distinctive orange-red under LW UV, helping to differentiate it from ruby even before a refractometer reading.

This table covers all 130 species in the GemID database, with expandable per-species notes for 19 gems where the response depends on color variety, diamond type, or treatment. Below the main table, the origin section breaks down ruby, sapphire, emerald, and spinel response by deposit and by synthetic growth method — the level of detail where the UV lamp starts separating natural from lab-grown material. For the filter tests that pair with the UV lamp, see the Chelsea & Hanneman filter chart.

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Gem	LW UV (365 nm)	SW UV (254 nm)	Notes
Danburite	Strong blue	Strong blue	—
Synthetic Color-Change Corundum	Strong red	Strong red	—
Synthetic Spinel	Strong Blue White	Strong Blue White	—
Amber	Strong blue	Moderate Blue White	—
Hackmanite	Strong orange-pink	Moderate Orange Pink	—
Kunzite	Strong orange	Moderate Orange	—
Howlite	Strong blue	Weak blue-white	—
Fluorite	Strong blue	Variable	—
Scapolite	Strong orange	Variable	—
Hauyne	Strong orange-pink	Inert	—
Pink Sapphire	Strong red	Inert	—
Alexandrite	Moderate Red	Inert	—
Padparadscha Sapphire	Moderate Orange Pink	Inert	—
Lapis Lazuli	Weak orange	Weak Yellow	—
Agate	Weak white/cream	Inert	—
Carnelian	Weak white/cream	Inert	—
Chalcedony	Weak white/cream	Inert	—
Charoite	Weak orange	Inert	—
Grossular Garnet	Weak orange	Inert	—
Ivory	Weak blue-white	Inert	—
Moonstone	Weak blue	Inert	—
Morganite	Weak Orange Pink	Inert	—
Rhodochrosite	Weak orange	Inert	—
Sunstone	Weak orange	Inert	—
Tanzanite	Weak Red Brown	Inert	—
Turquoise	Weak blue-white	Inert	—
Variscite	Weak Green	Inert	—
Zircon	Orange	Inert	Notes High zircon characteristically fluoresces yellow to orange-yellow under LW UV; dysprosium (Dy³⁺) and terbium (Tb³⁺) are the primary activators. This is relatively diagnostic — a strong mustard-yellow or orange-yellow LW response is a useful indicator of high-type zircon. SW UV fluorescence is also yellow-orange but typically weaker or inert. Green zircons tend to be inert; blue zircons show weak to moderate light blue LW response. Brown zircons inert to very weak red SW. Overall, colorless/pale and heat-treated stones show the strongest response. Low/metamict zircon (see zircon_low) shows weak to inert fluorescence due to radiation damage to the crystal lattice.
Apatite	Variable	Variable	Notes See LW notes. SW response is generally weaker than LW but still color-dependent and variable. Yellow apatite shows lilac-pink SW (weaker than LW). Blue apatite shows pale mauve SW. 'Variable' confirmed correct.
Opal	Variable	Variable	Notes SW UV response is also variable: commonly green or yellow in white/light opal, inert in black opal and most fire opal. Current value of 'inert' is incorrect as a blanket statement.
Ruby	Variable	Variable	Notes LW UV varies strongly by origin: Burmese/Mogok rubies typically moderate to strong red (high Cr, low Fe). Thai, Cambodian, and most African rubies are typically inert to weak red due to higher iron content, which quenches Cr³⁺ fluorescence. Mozambique rubies vary — some approach Burmese strength. Synthetic rubies (Verneuil, flux, hydrothermal) generally show strong red due to minimal Fe. Under LW UV a red-inhibiting filter may additionally reveal orange fluorescence. SW UV ranges from inert to strong red — generally weaker than LW response for the same stone. Fluorescence is a useful secondary indicator of geographic origin but not definitive; overlap exists.
Sphalerite	Variable	Variable	Notes Fluorescence is strongly variable and governed by iron content. Low-Fe specimens (cleiophane variety) fluoresce vividly under LW UV, typically orange to yellow-orange, occasionally blue; Mn²⁺ is the principal activator. High-Fe specimens are inert — iron quenches fluorescence. SW UV response follows the same pattern but is generally weaker. The correlation between low iron content, high sulfidation-state formation conditions, and strong orange LW fluorescence is well established.
Star Ruby	Variable	Variable	Notes Same fluorescence mechanism as faceted ruby — driven by Cr³⁺ concentration and Fe content, not the asterism-causing rutile inclusions. Burmese star rubies typically moderate to strong red LW UV; Thai and other iron-rich origins typically inert to weak. The rutile silk responsible for asterism does not contribute to or suppress fluorescence. SW UV: inert to moderate red, generally weaker than LW for same stone.
Topaz	Variable	Variable	Notes Fluorescence varies strongly by color variety. LW UV: colorless and blue topaz are inert to faint yellow-greenish; imperial/precious (orange-yellow) often strong yellow-orangy; pink variable. SW UV: pink shows weak brown; yellow shows weak orange-yellow; red shows weak yellow-brown; colorless/blue inert. Color variety must be known to predict fluorescence response.
Yellow Diamond	Variable	Variable	Notes Fluorescence depends critically on diamond type. Cape-series yellow diamonds (Type Ia, N3 center, showing 415 nm absorption line): strong blue fluorescence under both LW and SW UV — one of the most diagnostic fluorescence responses in gemology. May rarely show yellow phosphorescence after LW UV exposure. Canary yellow diamonds (Type Ib, isolated nitrogen): typically inert under both LW and SW UV, as they lack the N3 center. Lab-grown yellow (HPHT Type Ib or CVD): usually inert. Diamond type determination is needed to predict fluorescence response.
Brown Diamond	Variable	Inert	Notes Natural brown diamonds (Type Ia, color from plastic deformation or graining) are typically inert to weak blue under LW UV, and inert under SW UV. The brown coloration mechanism does not strongly activate fluorescent defect centers. HPHT-treated or irradiated brown diamonds may show different responses depending on treatment. Lab-grown CVD brown stones are generally inert under both LW and SW. Confidence medium — no single authoritative source found specifically for natural brown diamond fluorescence.
Diamond	Variable	Inert	Notes LW UV is highly variable but blue is by far the most common response in gem-quality colorless to near-colorless (D–Z) diamonds; GIA studies found approximately 25–35% of submitted diamonds show blue LW fluorescence. Cape series (yellow/brown, Type Ia with N3 center) commonly fluoresce blue LW and may show yellow phosphorescence afterward. Pink diamonds mostly fluoresce blue LW with yellowish to orangy phosphorescence. Blue diamonds (Type IIb) show rare orangy fluorescence. Green and brown diamonds often fluoresce green LW. Type IIa diamonds (rare, colorless, no nitrogen) are typically inert. SW UV reactions are generally much weaker or absent for all types. The blue SW response in some colorless diamonds (Cape series, N3 center) is diagnostically useful for separating from most simulants. Yellow and orange response under SW is rare but seen in some fancy-color stones.
Emerald	Variable	Inert	Notes Generally inert under both LW and SW UV. This is the dominant response across nearly all natural emerald origins due to iron content quenching Cr³⁺/V³⁺ fluorescence. Exception: low-iron Colombian emeralds (especially from Muzo and Chivor) may show weak to moderate red LW UV fluorescence — this is diagnostically useful as an indicator of Colombian origin, though not all Colombian stones fluoresce. Zhen'an (China) emeralds confirmed inert both LW and SW (G&G Winter 2025). Synthetic emeralds (Chatham, Gilson, hydrothermal) often show a red or orangy-red LW fluorescence, which can help distinguish them from most naturals.
Fire Opal	Variable	Inert	—
Malaya / Umbalite Garnet	Variable	Inert	Notes SW UV: inert. Pyralspite garnets (pyrope, spessartine, almandine series) do not fluoresce under shortwave UV. This is consistent across malaya garnet compositions.
Moissanite	Variable	Inert	Notes SW UV: inert for both natural and synthetic moissanite. See LW notes for generation-based nuance on older 6H synthetic material.
Pearl	Variable	Inert	Notes LW UV fluorescence varies significantly by pearl type: natural saltwater pearls typically show weak to moderate chalky blue-white; cultured akoya often weak to moderate blue-white; Tahitian/black pearls typically inert to moderate red-pink; freshwater cultured variable (weak blue-white to inert). Treated/brightened pearls may show strong blue-white LW response near 430–440 nm. SW UV typically inert to very weak across most types. Fluorescence response is diagnostically useful for separating natural vs. cultured and detecting optical brightening treatments.
Pink Diamond	Variable	Inert	—
Sapphire	Variable	Inert	Notes LW UV response is highly variety- and treatment-dependent: Blue natural sapphire is typically inert to weak orangy-red; colorless natural sapphire is inert to orangy-red; yellow/orange sapphire (especially synthetic) can show strong yellowish to reddish-orange; padparadscha sapphire may show weak to moderate orange, which is diagnostically useful. Blue synthetic corundum (sapphire) is typically inert LW. SW UV: natural blue and colorless sapphires are mostly inert, sometimes weak dark reddish; synthetic blue shows chalky blue-green; heat-treated blue sapphire colorless zones may show chalky blue-green SW. The orange LW fluorescence in padparadscha is a useful secondary test but not definitive alone. Iron suppresses fluorescence in blue sapphire similarly to ruby.
Spinel	Variable	Inert	Notes LW UV varies by color variety: Pink to red spinel: inert to red or red-orangy (Cr-bearing red spinel commonly shows strong red, similar to ruby; a useful separation point is that ruby tends to be stronger). Blue spinel (Fe-bearing): greenish fluorescence LW. Rare cobalt-blue spinel: weak to moderate red LW (diagnostic for cobalt coloration). Colorless and light green: inert to moderate orangy-red. Under X-ray, red/pink spinel shows moderate crimson glow; purple-mauve shows plum to lilac; some specimens respond green. SW UV: pink to red: inert to reddish; blue: inert; cobalt-blue: normally inert. The LW red fluorescence in red spinel can resemble ruby and should not be used alone for separation — use RI and crystal system.
Star Sapphire	Variable	Inert	—
Yellow Sapphire	Variable	Inert	—
Benitoite	Inert	Strong Blue White	—
Blue Diamond	Inert	Strong orange	—
Clinohumite	Inert	Strong orange	—
Almandine Garnet	Inert	Inert	—
Amazonite	Inert	Inert	—
Amethyst	Inert	Inert	—
Ametrine	Inert	Inert	—
Andalusite	Inert	Inert	—
Aquamarine	Inert	Inert	—
Aventurine	Inert	Inert	—
Black Opal	Inert	Inert	—
Black Spinel	Inert	Inert	—
Bloodstone	Inert	Inert	—
Cassiterite	Inert	Inert	—
Cat's Eye Chrysoberyl	Inert	Inert	—
Chrome Diopside	Inert	Inert	—
Chrome Tourmaline	Inert	Inert	—
Chrysoberyl	Inert	Inert	—
Chrysocolla	Inert	Inert	—
Chrysoprase	Inert	Inert	—
Cinnabar	Inert	Inert	—
Citrine	Inert	Inert	—
Color-Change Garnet	Inert	Inert	—
Color-Change Sapphire	Inert	Inert	Notes Color-change sapphires are generally inert under both LW and SW UV, consistent with natural blue sapphire behavior. Exceptions exist: some stones from Sri Lanka and Madagascar show a weak to moderate 'apricot' orange fluorescence under LW (and occasionally SW), attributed to unknown chromophore interaction; this is unaffected by heat treatment. Chromium-rich color-change stones (those with stronger red/purple component) may show very weak red LW fluorescence, similar to low-chrome ruby. Heat-treated color-change sapphires may show chalky blue-green SW fluorescence as a treatment indicator. No strong diagnostic fluorescence pattern exists for this variety as a class.
Coral	Inert	Inert	—
Cubic Zirconia	Inert	Inert	Notes CZ is generally inert under LW UV in routine gemological testing. Some specimens show a dull yellowish or whitish glow under LW UV, attributed to rare earth dopants (Y₂O₃ stabilizer, or minor Pr, Nd, Er used for coloring). Under SW UV, some CZ glows yellowish-green or beige; this is more common than a LW response. Inert is the expected result for colorless CZ in standard testing. Colored CZ varieties (especially pink, which may contain Er) are more likely to show a response. Practically: CZ fluorescence is not diagnostically useful as a positive indicator, but strong LW blue fluorescence would argue against CZ identification.
Cuprite	Inert	Inert	—
Demantoid Garnet	Inert	Inert	—
Diaspore	Inert	Inert	—
Enstatite	Inert	Inert	—
Goshenite	Inert	Inert	—
Grandidierite	Inert	Inert	—
Green Tourmaline	Inert	Inert	—
Hawk's Eye	Inert	Inert	—
Heliodor	Inert	Inert	—
Hematite	Inert	Inert	—
Hessonite Garnet	Inert	Inert	—
Hiddenite	Inert	Inert	—
Indicolite	Inert	Inert	—
Iolite	Inert	Inert	—
Jadeite	Inert	Inert	—
Jet	Inert	Inert	—
Kornerupine	Inert	Inert	—
Kyanite	Inert	Inert	—
Labradorite	Inert	Inert	—
Larimar	Inert	Inert	—
Low-Type Zircon	Inert	Inert	Notes Low (metamict) zircon is typically inert to very weak under both LW and SW UV. Radiation damage from radioactive decay of U and Th impurities progressively destroys the crystal lattice (metamictization), eliminating the ordered structure responsible for the strong lanthanide-activated fluorescence seen in high zircon. The amorphous, dark, pithy material characteristic of low-type zircon does not support efficient energy transfer to Dy³⁺/Tb³⁺ activators. Contrast with high zircon, which shows characteristic yellow-orange LW fluorescence.
Malachite	Inert	Inert	—
Moldavite	Inert	Inert	—
Nephrite	Inert	Inert	—
Obsidian	Inert	Inert	—
Onyx	Inert	Inert	—
Paraiba Tourmaline	Inert	Inert	—
Peridot	Inert	Inert	—
Phenakite	Inert	Inert	—
Pietersite	Inert	Inert	—
Prasiolite	Inert	Inert	—
Prehnite	Inert	Inert	—
Pyrope Garnet	Inert	Inert	—
Rainbow Moonstone	Inert	Inert	—
Red Beryl	Inert	Inert	—
Rhodolite Garnet	Inert	Inert	—
Rhodonite	Inert	Inert	—
Rock Crystal	Inert	Inert	—
Rose Quartz	Inert	Inert	—
Rubellite	Inert	Inert	—
Serpentine	Inert	Inert	—
Sinhalite	Inert	Inert	—
Smoky Quartz	Inert	Inert	—
Sodalite	Inert	Inert	—
Spessartite Garnet	Inert	Inert	—
Sphene	Inert	Inert	—
Star Diopside	Inert	Inert	—
Star Garnet	Inert	Inert	—
Sugilite	Inert	Inert	—
Taaffeite	Inert	Inert	—
Thulite	Inert	Inert	—
Tiger's Eye	Inert	Inert	—
Tourmaline	Inert	Inert	—
Tsavorite Garnet	Inert	Inert	—
Watermelon Tourmaline	Inert	Inert	—
White Sapphire	Inert	Inert	—
YAG	Inert	Inert	—

Click a column header to re-sort the table.

Fluorescence by Origin — Natural vs. Synthetic

For emerald, ruby, sapphire, spinel, the UV response varies by geographic origin and by growth method — often enough to matter. A synthetic grown with little iron can fluoresce strongly where its iron-rich natural counterpart stays inert, so the lamp is frequently the first hint that a stone deserves closer inspection. Responses below are indicators, not proof of origin.

Emerald

Origin / Growth Method	LW UV (365 nm)	SW UV (254 nm)	Notes
Natural Colombian	Inert	Inert	Despite high Cr content, Fe quenching makes Colombian emerald inert — confirmed by GIA G&G Winter 2025.
Natural Zambian	Inert	Inert	—
Natural Brazilian	Inert	Inert	—
Natural Zimbabwe Sandawana	Inert	Inert	—
Natural Afghan	Inert	Inert	—
Synthetic — Flux	Moderate Red	Weak red	Flux emeralds (Chatham, Gilson) can show strong red LW UV — a key differentiator from natural.
Synthetic — Hydrothermal	Inert to weak	Inert	Hydrothermal synthetics generally weaker response than flux.
Synthetic — Lechleitner	Inert to weak	Inert	Lechleitner (beryl core + synthetic overgrowth) — variable; core influences response.

Ruby

Origin / Growth Method	LW UV (365 nm)	SW UV (254 nm)	Notes
Burmese Mogok	Strong red	Strong red	Mogok fluorescence can be so strong it causes daylight fluorescence (face-up red glow in sunlight). Classic high-Cr, low-Fe deposit.
Thai Cambodian	Inert to weak	Inert	High Fe content quenches Cr fluorescence.
African Mozambique	Weak red	Weak red	Intermediate Fe content vs Burma/Thailand; Montepuez material often stronger than Thai but weaker than Mogok.
Sri Lankan	Moderate Red	Weak red	Lower Fe than Thai, higher than Mogok; moderate response.
Vietnamese Luc Yen	Strong red	Strong red	Similar to Burmese Mogok — low Fe deposits; vivid red fluorescence.
African Tanzania	Inert to weak	Inert	High Fe, similar to Thai material; fluorescence strongly quenched.
Synthetic — Flame Fusion	Strong red	Strong red	Low Fe (no natural inclusions), Cr dominant — mimics Burmese; very strong, often chalky quality.
Synthetic — Flux	Strong red	Strong red	Low Fe, Cr dominant; similar to flame fusion but LW typically exceeds SW.
Synthetic — Hydrothermal	Moderate Red	Weak red	May vary by manufacturer; generally less intense than flame fusion or flux.
Synthetic — Czochralski	Strong red	Strong red	High purity, Cr dominant; extremely intense — near-blinding fluorescence reported.

Sapphire

Origin / Growth Method	LW UV (365 nm)	SW UV (254 nm)	Notes
Natural Blue Kashmir	Inert	Inert	Classic Kashmir sapphire is inert — useful negative indicator.
Natural Blue Burmese	Inert to weak	Inert	Mogok blue sapphire generally inert; occasional weak orange.
Natural Blue Sri Lankan	Inert to weak	Inert	Generally inert; some stones weak orange LW.
Natural Blue Australian	Inert	Inert	High Fe Australian sapphire — completely inert.
Natural Blue Thai Cambodian	Inert	Inert	High Fe — inert.
Natural Blue Montana	Inert	Inert	—
Natural Padparadscha	Weak orange	Inert	Padparadscha orange LW fluorescence can be a useful confirmatory indicator alongside color.
Natural Yellow	Inert	Inert	Fe-colored yellows are inert. Exception: some Ceylon yellow show weak orange.
Natural Color Change	Inert	Inert	—
Synthetic — Flame Fusion	Inert	Inert	Verneuil blue sapphire — no Cr, low impurities — inert.
Synthetic — Flux	Inert	Inert	—
Synthetic — Hydrothermal	Inert	Inert	—
Synthetic — Czochralski	Inert	Inert	—

Spinel

Origin / Growth Method	LW UV (365 nm)	SW UV (254 nm)	Notes
Natural Red Pink	Moderate Red	Inert to weak	Red/pink spinel Cr content drives LW fluorescence; intensity varies with Fe content. Transparent, glowing quality (not chalky).
Natural Blue	Inert	Inert	Fe-dominant chromophore; no Cr — completely inert under both LW and SW UV.
Natural Colorless White	Inert	Inert	No chromophore activators; typically inert.
Natural Orange	Orange	Inert	Mn²⁺ activator drives orange LW fluorescence; SW typically inert.
Natural Violet Purple	Inert to weak	Inert	Mixed Cr/Fe — Fe quenches fluorescence; weak at best under LW.
Synthetic — Flame Fusion	Inert	Inert	Flame fusion synthetic spinel was a common diamond simulant — always inert; lacks Cr, produced as colorless or cobalt-blue.
Synthetic — Flux	Inert to weak	Inert	Red flux-grown spinel may show weak LW response if Cr is present; generally weak.

Which gemstones fluoresce under UV light?
27 of the 130 species in this chart show a weak-or-stronger longwave UV response; the rest are inert or variable. The strongest responders sort to the top of the table.

Do natural and synthetic gemstones fluoresce differently?
Often, yes — because fluorescence depends on trace chemistry, and growth environments differ. For ruby, this chart records Burmese (Mogok) stones as strong red under LW while iron-rich Thai/Cambodian stones are inert to weak, and flame-fusion synthetics as strong red. See the by-origin tables below the main chart for ruby, sapphire, emerald, and spinel.

What is the difference between LW and SW UV?
Longwave UV is approximately 365 nm (the common "black light"); shortwave UV is approximately 254 nm and requires a dedicated SW lamp with safety precautions — SW light damages eyes and skin. Many stones respond differently under the two wavelengths, and the pair of responses together is more diagnostic than either alone.

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Gemstone Fluorescence Under UV Light — LW and SW Reference

Fluorescence by Origin — Natural vs. Synthetic

Emerald

Ruby

Sapphire

Spinel