Key properties
| Chemical formula | CaCO3 (as aragonite and/or calcite) with conchiolin (organic binder) and water |
| Crystal system | None (polycrystalline biological aggregate) |
| Mohs hardness | 3.5 |
| Toughness | Fair; nacreous shell fair to good, chalky types poor |
| Refractive index | 1.530-1.685 |
| Birefringence | 0.1550 |
| Optic character | Aggregate (AGG); strong birefringence blink across the aragonite/calcite range |
| Specific gravity | 2.70-2.89 |
| Cleavage | None |
| Fracture | Uneven to splintery |
| Habit | Not applicable; layers laid down by the mantle - nacreous (platy, pearly), prismatic (porcellaneous) or crossed-lamellar |
| Lustre | Dull on rough material; pearly, greasy or vitreous where nacreous; polish: Pearly to vitreous (nacre); porcellaneous on conch-type shell |
| UV fluorescence | Variable depending on shell type; sometimes weak blue to whitish, not diagnostic |
| Pleochroism | None |
| Cause of colour | Body colour from organic pigments in the shell layers; iridescence (orient) is interference of light reflected from stacked platy aragonite layers of nacre |
| Typical inclusions | Diagnostic layered, banded or fibrous growth structure parallel to the shell surface; nacre shows overlapping platy tiles; conch shell shows flame-like fibrous structure; operculum has an eye-like spiral; cameos show layer boundaries |
| Stability | Fair. Blackens under a jeweller's torch; attacked by all acids (effervesces in dilute hydrochloric acid); dries out and becomes brittle; some dyed or faded colours change in light |
| Heat sensitivity | Moderate-high; organic binder degrades and the carbonate blackens/burns |
| Care and cleaning | Warm soapy water, soft brush; never ultrasonic or steam; rinse and dry promptly. Keep away from acids - even vinegar and citrus etch the surface |
| Birthstones | None (mother-of-pearl is the traditional 1st wedding anniversary gift in some lists) |
| Availability | Plentiful; most jewellery shell comes from tropical and subtropical seas as a food-fishery by-product. Some species (queen conch, giant clam, abalone) are CITES-regulated |
| Recognition | Everyday familiarity: mother-of-pearl buttons and inlay, conch and abalone jewellery, shell cameos, operculum 'cat's-eyes' |
Varieties (4)
Conch Shell
| Colour | porcellaneous pink, salmon, orange-peach and cream, often deeper toward the lip |
| Transparency | opaque |
| Clarity type | Opaque |
| Phenomena | None in shell (the rare conch 'pearl' shows flame structure - see calcareous concretions) |
| Appearance | Smooth porcelain-pink material with subtle wavy flame-like fibrous structure; takes a soft waxy-porcellaneous polish |
| Trade names | queen conch (Aliger/Strombus gigas) • conch • pink conch • carnavalia (cameo-grade conch) |
| Misnomers | 'conch pearl' for the non-nacreous conch concretion (accepted trade usage, technically a calcareous concretion) |
| Typical sizes | Whole shells up to about 30 cm; beads 6-20 mm; pendants and carved sections of several centimetres |
| Cutting styles | Whole polished shells, beads, cabochons, pendants, carvings, buttons; shell fragments as inlay |
| Key separations | vs pink coral: coral shows polyp cavities/tubular fibrous structure and slightly higher SG; conch is layered porcelain with flame structure. vs dyed howlite/other rock: shell effervesces in dilute HCl, howlite does not, and dye sits in howlite's veins. vs pink shell imitations in plastic: plastic gives no acid reaction, no layered structure, smooth on teeth |
| Sources (localities) | Caribbean: Bahamas, Turks and Caicos, Venezuela, Honduras, Florida Keys • queen conch is CITES Appendix II - international trade controlled but permitted with permits |
| Availability | Plentiful as food-fishery by-product, subject to CITES export paperwork |
| Market notes | Conch is genuinely farmed/fished for food, so supply is stable; disclose CITES status for cross-border shipments. Conch 'pearls' are a separate, far rarer product |
| Care notes | Warm soapy water only; no acids, perfume or chlorine; fades very slowly in strong light; store away from harder gems |
| In short | Queen conch shell from the Caribbean is the classic pink porcellaneous jewellery shell, soft, layered and faintly flame-structured, with rare conch 'pearls' as its precious by-product. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.50–5.00 | $0.10 – $1.00 | beads, cabochons, carvings | 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.
Shell — Red-Pink
| Colour | pink to orange-red porcellaneous layers, often white-on-red banded as in cameo shells |
| Transparency | opaque |
| Clarity type | Opaque, layered |
| Phenomena | None (occasional weak sheen) |
| Appearance | Banded red-pink and white shell; cameos show a pale figure carved in relief on a pigmented ground |
| Trade names | conch shell (pink-orange) • helmet shell (cameo shell, white on brown/orange layers) • carnelian shell • red urchin spine beads |
| Misnomers | shell cameos sold as 'coral cameos' • dyed shell beads sold as coral • operculum sold as 'Chinese cat's-eye' |
| Typical sizes | Cameo blanks 2-10 cm; beads 6-15 mm; large pieces common |
| Cutting styles | Cameos (helmet/conch), beads, cabochons, inlay, carved flowers |
| Key separations | vs coral: coral has polyp structure, no layer banding; shell cameos show layer boundaries and a concave back (natural shell curve). vs dyed howlite or dyed shell: dye pools in cracks; howlite does not effervesce in dilute acid. vs plastic cameos: moulded plastic lacks tool marks, has rounded detail and mould seams, hot point melts |
| Sources (localities) | Tropical seas worldwide: Caribbean conch and helmet shell • Mediterranean (Rome/ Naples cameo tradition) • Indo-Pacific helmet and cassid shells |
| Availability | Plentiful; cameo carving concentrated in Italy (Torre del Greco) and Asia |
| Market notes | Sell shell cameos on their own merits (durable, affordable) and against coral cameos (rarer, pricier); always disclose dye |
| Care notes | Warm soapy water; cameo brushes soften with soaking - wipe instead; keep from acids and heat |
| In short | Red-pink shells - conch for colour, helmet for banded cameo blanks - supply the cameo trade and coral look-alikes at friendly prices. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.50–5.00 | $0.10 – $2.00 | beads and cameos | 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.
Mother-of-Pearl
| Colour | silvery white to cream with soft pink-blue-green orient; gold-lip and black-lip varieties tinted |
| Transparency | opaque |
| Clarity type | Opaque, nacreous |
| Phenomena | Orient (iridescence) |
| Appearance | Shimmering pearly sheets or beads; the same nacre that coats pearls, shown as a surface |
| Trade names | mother-of-pearl (MOP) • nacre • white-lip, gold-lip and black-lip shell (Pinctada oyster) • freshwater mussel shell (Mississippi) • Trochus button shell |
| Misnomers | 'pearl shell' sold as pearl • 'paua' used loosely for any iridescent shell (true paua is abalone) |
| Typical sizes | Large sheets and blanks of many centimetres; beads 4-16 mm; watch-dial discs |
| Cutting styles | Buttons (historic), beads, cabochons, inlay and marquetry, watch dials, bead nuclei for cultured pearls, mosaic tiles |
| Key separations | vs plastic 'pearl' imitations: mother-of-pearl feels gritty rubbed against the tooth, shows true layered nacre at the edge or drill hole, SG about 2.86 vs plastic about 1.3. vs glass imitation pearl: coating flakes at drill holes to show glass core; glass is smooth on teeth. vs iridescent coated glass/titanium 'mystic' shell imitations: coating scratches off |
| Sources (localities) | Pearl oyster shell (Pinctada maxima, margaritifera) from Australia, Indonesia, Philippines, French Polynesia • freshwater mussel from Mississippi/Tennessee river systems (historically the button capital) • Trochus and abalone from Indo-Pacific |
| Availability | Plentiful; by-product of the pearl and food fisheries; CITES rules apply to some oyster and mussel trade |
| Market notes | The bread-and-butter iridescent material for casual jewellery and watch dials; dyed and laminate products should be disclosed; pearl-farm by-product gives it a good sustainability story |
| Care notes | Warm soapy water; avoid acids, perfume and prolonged strong light; ultrasonic risky |
| In short | Mother-of-pearl is the nacreous lining of pearl oysters, mussels and abalone: tough, shimmering sheets of aragonite platelets used for beads, buttons, inlay and dials. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.50–5.00 | $0.05 – $0.50 | beads, inlay, buttons | 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.
Dark / Iridescent Shell
| Colour | dark grey to brown-black body with vivid blue, green, violet and pink iridescence |
| Transparency | opaque |
| Clarity type | Opaque |
| Phenomena | Orient/iridescence |
| Appearance | Dark shell flashing peacock blue-green-violet; abalone shows waving bands of colour inside a rough exterior |
| Trade names | abalone / paua (Haliotis) • black-lip mother-of-pearl (Pinctada margaritifera) • black mabe shell • 'paua shell' |
| Misnomers | 'black opal shell' promotional names • abalone doublets sold as solid |
| Typical sizes | Abalone shells 10-20 cm yield substantial blanks; black-lip oyster 15-25 cm; large pieces common |
| Cutting styles | Inlay and marquetry, cabochons, freeform pendants, watch dials, doublets and triplets (thin nacre capped with resin or quartz) |
| Key separations | vs ammolite: ammolite's iridescence sits on a fossil ammonite shell in tessellated 'dragon-skin' patches and is opaque; abalone shows wavy banded nacre and shell curves. vs labradorite: feldspar is translucent at edges, one cleavage plane flash, SG 2.7, hardness 6. vs coated glass 'rainbow' imitations: coating scratches off, no nacre layers. vs opal: opal shows play-of-colour from silica spheres, patchy in depth, no layered nacre |
| Sources (localities) | Abalone/paua: New Zealand (paua), Australia, California, Mexico, South Africa, Japan • black-lip oyster: French Polynesia, Cook Islands, Okinawa • some abalone fisheries regulated; New Zealand paua quota-managed |
| Availability | Plentiful but fishery-managed; paua export from New Zealand is strictly quota-controlled |
| Market notes | Thin abalone nacre is almost always capped (doublet) for durability - disclose assembled products; dyed dark shell also common |
| Care notes | Warm soapy water only; no ultrasonic, steam, acids or solvents (resin caps can cloud); hard wear can pop caps |
| In short | Dark iridescent shells - abalone above all - trade on their peacock flash of blue-green nacre, usually as inlay or capped doublets from managed fisheries. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.50–5.00 | $0.10 – $2.00 | inlay, cabochons, doublets | 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
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 #31 · gem #32 · gem #145 · gem #189 · gem #214
Related materials: Corundum · Diamond · Opal · Quartz · Spinel · Topaz
Identification wizard · All 83 materials · Singapore gem labs