Key properties
| Chemical formula | CaCO3 (mostly aragonite, some calcite) with conchiolin binder and 2-4% water |
| Crystal system | None (aggregate of microscopic aragonite platelets in an organic matrix) |
| Mohs hardness | 2.5-4.5 |
| Toughness | Usually good but variable; the surface nacre is easily scratched and aged or dehydrated pearls can flake and crack |
| Refractive index | 1.520-1.690 |
| Birefringence | 0.1550 |
| Optic character | Aggregate (AGG); strong birefringence blink across the nacre |
| Specific gravity | 2.60-2.85 |
| Cleavage | None |
| Fracture | Uneven; nacre flakes in layers |
| Habit | Not applicable; naturally rounded, baroque, button or drop forms grown within the mollusc |
| Lustre | Pearly (nacreous) to dull; the finest approach a metallic mirror sheen; polish: Not polished - the nacre surface is the lustre (near dull to almost metallic in fine pearls) |
| UV fluorescence | Variable: inert to strong light blue, yellow, green or pink in LW and SW; natural-colour dark pearls weak to moderate red to orangy-red in LW (dyed blacks are inert) |
| Pleochroism | None |
| Cause of colour | Bodycolour from organic pigments (conchiolin and related compounds) plus pore/platelet scattering; overtones and orient come from interference and diffraction of light on the stacked aragonite platelets of the nacre |
| Typical inclusions | Internal structure invisible to the loupe - the proof of natural vs cultured is in the X-radiograph: natural pearls show concentric growth rings to the centre; bead-cultured pearls show a plain shell bead with a thin nacre skin |
| Stability | Attacked by all acids - perspiration, perfume, hairspray and vinegar dissolve nacre; dehydration (display-case heat) cracks nacre; stable to light; burns under flame |
| Heat sensitivity | High: turns brown, splits and cracks; even prolonged moderate heat dries and crazes nacre |
| Care and cleaning | Wipe with a soft cloth after every wearing; occasionally mild soap and water, drying the string fully. Never ultrasonic or steam. Last on, first off - after perfume and hairspray |
| Birthstones | June (with alexandrite and moonstone); 3rd and 30th wedding anniversaries |
| Availability | Natural pearls scarce - very few reach the market today. Cultured pearls plentiful across every price level, from Chinese freshwater to South Sea |
| Recognition | Universal - the best-known organic gem; quality described by the GIA 7 value factors: size, shape, colour, lustre, surface, nacre, matching |
Varieties (4)
Natural Pearl
| Colour | white and cream bodycolours with rose (pink), green or blue overtones; naturals also occur in yellow, grey and fancy colours |
| Transparency | opaque |
| Clarity type | Opaque |
| Phenomena | Orient (faint iridescence); baroque naturals may show strong orient |
| Appearance | Warm, satiny nacre; often slightly off-round or baroque because no nucleus guided the shape; older naturals can show soft worn lustre |
| Trade names | Oriental pearls (Persian Gulf naturals) • Ceylon/Madras • Australian 'silvery' • Venezuelan (yellow-white) • seed pearls (under about 2 mm) • dust pearls • baroque • hinge/dogtooth freshwater shapes • maiden pearls (newly fished) |
| Misnomers | 'French pearl' (a shell fragment, not a pearl) • 'blister pearl' is strictly a shell-attached dome, not a whole pearl |
| Typical sizes | Rounds usually 2-9 mm; South Sea naturals over 7 mm are rare and prized; baroques occasionally exceed 15-50 mm in longest dimension |
| Cutting styles | Rarely cut: drilled whole for necklaces, half-drilled for mounting; half pearls sawn in half; blister domes cut from the shell |
| Key separations | vs cultured pearl: X-radiography shows concentric rings to centre (natural) vs a round bead with thin nacre rind (cultured); supported by X-ray fluorescence and drill-hole/candling clues. vs glass imitation: imitations are smooth on the teeth (nacre is gritty), coating flakes at drill holes, no birefringence blink. vs plastic: smooth, light (SG about 1.3 vs about 2.7), warm to touch instantly |
| Sources (localities) | Persian Gulf (Bahrain 'Basra' - the classic oriental fishery) • Sri Lanka (Gulf of Mannar) • Red Sea • Venezuela (Margarita) • Gulf of California (La Paz) • north-west Australia • Tahiti (natural blacks) • freshwater: Mississippi basin, Scottish rivers (historical), China |
| Availability | Scarce: commercial natural fisheries have essentially ceased; naturals appear mainly at auction, in antique jewellery and from accidental by-catch |
| Market notes | Every claimed natural pearl should be X-ray verified (a lab report) before sale; prices are set pearl-by-pearl at auction rather than per a tariff. Disclose any drilling repairs or peeling |
| Care notes | Wipe after wear; keep away from acids, perfume, hairspray and perspiration; restring knotted strands regularly; store flat and separate from harder gems |
| In short | Natural pearls - accidental, all-nacre, mostly antique - are the connoisseur's pearl, verified only by X-ray structure and sold pearl by pearl. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.10–1.00 | $100.00 – $2000.00 | antique strands, seed and baroque naturals | 2026-10-26 |
| 1.00–10.00 | $1000.00 – $10000.00 | fine round naturals | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Natural Dark Pearl
| Colour | black, dark grey, and dark tones of blue, purple, green or bronze, usually with rosé, green or blue overtones |
| Transparency | opaque |
| Clarity type | Opaque |
| Phenomena | Orient; the prized 'peacock' green-purple overtone |
| Appearance | Sombre grey-black with metallic sheen and shifting rosé/ green/ blue overtones; naturals usually baroque or drop |
| Trade names | La Paz pearls (Gulf of California) • Tahitian/Pacific naturals • black pearls • peacock (overtone grade) |
| Misnomers | 'black pearl' applied to dyed pale pearls • 'Bombay blacks' (historically dyed) |
| Typical sizes | Most naturals under 10 mm; a fine round natural black over 10 mm is a museum piece |
| Cutting styles | Drilled whole; rarely cut |
| Key separations | vs dyed black cultured pearl: LW UV - natural blacks glow weak-moderate red, silver-nitrate or organic dyes are inert; dye also concentrates at drill holes and flaws. vs cultured black: X-radiograph structure. vs dark conch/melo concretion: non-nacreous, no orient, SG about 2.85 |
| Sources (localities) | Gulf of California, Mexico (La Paz/Panja) • Tahiti and French Polynesia (Pinctada margaritifera) • Panama • Fiji; historic 'black' fisheries exhausted |
| Availability | Extremely scarce; essentially antique or rare by-catch |
| Market notes | Verify colour origin and natural origin by lab report; naturally dark naturals are among the most valuable pearls at auction |
| Care notes | As all pearls: acids, perfume and perspiration attack nacre; wipe and store separately |
| In short | Naturally dark pearls - grey-black with rosé and peacock overtones - are among the rarest pearls; their soft red LW-UV glow separates them from dyed blacks. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.20–2.00 | $500.00 – $5000.00 | antique and by-catch naturals | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Cultured Pearl
| Colour | white, cream and silver bodycolours with rosé, cream, green or blue overtones; fancy golds, peaches and pastel dyed/treated colours |
| Transparency | opaque |
| Clarity type | Opaque |
| Phenomena | Orient; lustre is the primary value driver |
| Appearance | Bright, evenly rounded nacre, typically rounder and more lustrous than naturals thanks to the round bead and controlled husbandry |
| Trade names | Akoya (Japan/China saltwater) • South Sea (white and golden, Australia/Indonesia/Philippines) • Tahitian (French Polynesia) • freshwater (China) • Biwa (historic Japanese lake) • keshi (spontaneous all-nacre cultured by-product) • mabe (assembled blister dome) • Edison (bead-nucleated freshwater) |
| Misnomers | 'Biwa' used for any freshwater pearl • 'Majorica'/shell 'pearls' are coated shell beads, not pearls at all • 'seed pearl' for tiny cultured freshwater |
| Typical sizes | Akoya 3-9 mm • South Sea 8-20 mm • Tahitian 8-17 mm • freshwater 2-16 mm (baroques larger); GIA cites cultured range 2-16 mm |
| Cutting styles | Whole drilled; half-drilled for rings/pendants; mabe assembled domes; rarely cut |
| Key separations | vs natural pearl: X-radiography (bead + nacre rind vs concentric rings), X-ray fluorescence, candling stripes. vs imitation 'pearls' (glass, shell, plastic): tooth test gritty, birefringence blink, layered nacre visible in drill hole, SG about 2.7; coated imitations flake at the drill hole |
| Sources (localities) | China (freshwater - Zhuji region; Akoya - Beihai/Guangxi) • Japan (Akoya - Mie, Ehime; remaining Biwa tradition) • Australia (South Sea - Broome) • Indonesia and Philippines (South Sea gold/white) • French Polynesia (Tahitian black) • US (freshwater by-product) |
| Availability | Plentiful overall; fine-quality South Sea and Tahitian annual output genuinely limited |
| Market notes | Always disclose cultured origin and treatments (bleaching, dyeing, irradiation, coating); 'pearl' legally means natural unless qualified by 'cultured' in many jurisdictions. Nacre thickness drives durability - thin-skinned Akoya can flake |
| Care notes | Last on first off; wipe after wear; mild soapy water only, dry string fully; never ultrasonic/steam; store separately from harder stones |
| In short | Cultured pearls - farmed nacre grown around a planted bead or tissue piece - are the modern pearl market, from inexpensive Chinese freshwater to Australian South Sea giants. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.20–1.00 | $1.00 – $50.00 | freshwater commercial to fine | 2026-10-26 |
| 0.50–3.00 | $50.00 – $500.00 | fine Akoya | 2026-10-26 |
| 3.00–15.00 | $150.00 – $1500.00 | South Sea white/gold | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Cultured Dark Pearl
| Colour | natural grey-black range from Tahitian farms (aubergine, peacock, silver-grey) plus dyed black and treated 'chocolate' pearls |
| Transparency | opaque |
| Clarity type | Opaque |
| Phenomena | Orient; peacock (green-rosé) overtone most prized |
| Appearance | Grey to black nacre with metallic sheen and shifting overtones; rounds to drops and baroques |
| Trade names | Tahitian cultured pearl • black South Sea • peacock • aubergine • chocolate pearls (treated) • 'black Akoya' (usually dyed) |
| Misnomers | 'black pearls' that are dyed pale pearls • 'Madagascar blacks' promotional names |
| Typical sizes | 8-17 mm typical for Tahitian; dyed freshwater blacks 6-12 mm |
| Cutting styles | Whole drilled, half-drilled; strands, pendants, drops |
| Key separations | vs natural dark pearl: X-radiography (bead nucleus) plus the natural's stronger red LW fluorescence. vs dyed pearl: inert LW UV, dye at drill holes. vs dark shell beads/'shell pearls': smooth, no blink, uniform perfection. vs dark conch pearl: nacreous lustre vs porcellaneous flame |
| Sources (localities) | French Polynesia (Gambier and Tuamotu archipelagos - the regulated 'Tahitian' appellation) • Cook Islands • Fiji (exotic colours) • dyed blacks usually from Chinese freshwater or Akoya stock |
| Availability | Steady but limited - Tahitian output is capped by farming cycles; natural-colour export minimum nacre thickness regulated by French Polynesia |
| Market notes | Disclose any dyeing or irradiation; 'Tahitian' is a protected appellation for Polynesian P. margaritifera cultured pearls; chocolate/champagne treated colours should be labelled treated |
| Care notes | As all pearls: no acids/perfume/heat; wipe after wear; knotted restringing for strands |
| In short | Cultured dark pearls are mainly Tahitian black-lip farm pearls in natural greys and peacock overtones, alongside dyed and treated darks that must be disclosed. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.50–3.00 | $30.00 – $300.00 | dyed and commercial Tahitian | 2026-10-26 |
| 3.00–12.00 | $150.00 – $1500.00 | fine round Tahitian with peacock overtone | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #142 · gem #143 · gem #187 · gem #188 · gem #212 · gem #213
Related materials: Corundum · Diamond · Opal · Quartz · Spinel · Topaz
Identification wizard · All 83 materials · Singapore gem labs