The iridescent nacre inside a Nautilus shell.

Nacre ( also ),[1] also known as mother of pearl, is an organic-inorganic composite material produced by some molluscs as an inner shell layer; it also makes up the outer coating of pearls. It is strong, resilient, and iridescent.

Nacre is found in some of the more ancient lineages of bivalves, gastropods, and cephalopods. However, the inner layer in the great majority of mollusc shells is porcellaneous, not nacreous, and this usually results in a non-iridescent shine, or more rarely in non-nacreous iridescence such as flame structure as is found in conch pearls.

The outer layer of pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Other mollusc families that have a nacreous inner shell layer include marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.


  • Physical characteristics 1
    • Structure and appearance 1.1
    • Formation 1.2
    • Function 1.3
    • In different mollusc groups 1.4
  • Commercial sources 2
  • Decorative uses 3
    • Architecture 3.1
    • Fashion 3.2
    • Musical instruments 3.3
    • Other 3.4
  • Manufactured nacre 4
  • See also 5
  • References 6
  • Further reading 7
  • External links 8

Physical characteristics

Structure and appearance

Schematic of the microscopic structure of nacre layers
Electron microscopy image of a fractured surface of nacre

Nacre is composed of hexagonal platelets of elastic biopolymers (such as chitin, lustrin and silk-like proteins). This mixture of brittle platelets and the thin layers of elastic biopolymers makes the material strong and resilient, with a Young's modulus of 70 GPa (when dry).[3] Strength and resilience are also likely to be due to adhesion by the "brickwork" arrangement of the platelets, which inhibits transverse crack propagation. This structure, at multiple length sizes, greatly increases its toughness, making it almost as strong as silicon.

Nacre appears iridescent because the thickness of the aragonite platelets is close to the wavelength of visible light. These structures interfere constructively and destructively with different wavelengths of light at different viewing angles, creating structural colours.

The crystallographic c-axis points approximately perpendicular to the shell wall, but the direction of the other axes varies between groups. Adjacent tablets have been shown to have dramatically different c-axis orientation, generally randomly oriented within ~20° of vertical.[4][5] In bivalves and cephalopods, the b-axis points in the direction of shell growth, whereas in the

  • Objects with mother-of-pearl in the Staten Island Historical Society Online Collections Database

External links

  • Frýda, J.; Bandel, K.; Frýdová, B. (2009). "Crystallographic texture of Late Triassic gastropod nacre: evidence of long-term stability of the mechanism controlling its formation".  
  • Lin, A.; Meyers, M.A. (2005-01-15). "Growth and structure in abalone shell".  
  • Mayer, G. (2005). "Rigid biological systems as models for synthetic composites". Science 310 (5751): 1144–1147.  
  • Bruet, B.; Qi, H.J.; Boyce, M.C.; Panas, R.; Tai, K.; Frick, L.; Ortiz, C. (2005). "Trochus niloticus"Nanoscale morphology and indentation of individual nacre tablets from the gastropod mollusc (PDF). J. Mater. Res. 20 (9): 2400.  
  • Antonio G. Checa, Julyan H. E. Cartwright, Marc-Georg Willinger and Steven M. Stanley, The Key Role of the Surface Membrane in Why Gastropod Nacre Grows in Towers; Proceedings of the National Academy of Sciences of the United States of America, Vol. 106, No. 1, Jan. 6, 2009

Further reading

  1. ^ Definition of nacre at
  2. ^ a b Nudelman, Fabio; Gotliv, Bat Ami; Addadi, Lia; Weiner, Steve (2006). "Mollusk shell formation: Mapping the distribution of organic matrix components underlying a single aragonitic tablet in nacre". Journal of Structural Biology 153 (2): 176–87.  
  3. ^ Jackson, A. P.; Vincent, J. F. V; Turner, R. M. (1988). "The mechanical design of nacre". Proceedings of the Royal Society B: Biological Studies (The Royal Society, published 22 Sep 1988) 234 (1277): 415–440.  
  4. ^ Metzler, Rebecca; Abrecht, Mike; Olabisi, Ronke; Ariosa, Daniel; Johnson, Christopher; Frazer, Bradley; Coppersmith, Susan; Gilbert, PUPA (2007). "Architecture of columnar nacre, and implications for its formation mechanism". Physical Review Letters 98 (26): 268102.  
  5. ^ Olson, Ian; Kozdon, Reinhard; Valley, John; Gilbert, PUPA (2012). "Mollusk shell nacre ultrastructure correlates with environmental temperature and pressure". Journal of the American Chemical Society 134 (17): 7351–7358.  
  6. ^ a b c d Checa, Antonio G.; Ramírez-Rico, Joaquín; González-Segura, Alicia; Sánchez-Navas, Antonio (2008). "Nacre and false nacre (foliated aragonite) in extant monoplacophorans (=Tryblidiida: Mollusca)". Naturwissenschaften 96 (1): 111–22.  
  7. ^ Katti, Kalpana S.; Katti, Dinesh R.; Pradhan, Shashindra M.; Bhosle, Arundhati (2005). "Platelet interlocks are the key to toughness and strength in nacre". Journal of Materials Research 20 (5): 1097.  
  8. ^ Ghosh, Pijush; Katti, Dinesh R.; Katti, Kalpana S. (2008). "Mineral and Protein-Bound Water and Latching Action Control Mechanical Behavior at Protein-Mineral Interfaces in Biological Nanocomposites". Journal of Nanomaterials 2008: 1.  
  9. ^ Mohanty, Bedabibhas; Katti, Kalpana S.; Katti, Dinesh R. (2008). "Experimental investigation of nanomechanics of the mineral-protein interface in nacre". Mechanics Research Communications 35: 17.  
  10. ^ Ghosh, Pijush; Katti, Dinesh R.; Katti, Kalpana S. (2007). "Mineral Proximity Influences Mechanical Response of Proteins in Biological Mineral−Protein Hybrid Systems". Biomacromolecules 8 (3): 851–6.  
  11. ^ Jackson, D. J.; McDougall, C.; Woodcroft, B.; Moase, P.; Rose, R. A.; Kube, M.; Reinhardt, R.; Rokhsar, D. S.; et al. (2009). "Parallel Evolution of Nacre Building Gene Sets in Molluscs". Molecular Biology and Evolution 27 (3): 591–608.  
  12. ^ Addadi, Lia; Joester, Derk; Nudelman, Fabio; Weiner, Steve (2006). "Mollusk Shell Formation: A Source of New Concepts for Understanding Biomineralization Processes". ChemInform 37 (16).  
  13. ^ Schäffer, Tilman; Ionescu-Zanetti, Cristian; Proksch, Roger; Fritz, Monika; Walters, Deron; Almquist, Nils; Zaremba, Charlotte; Belcher, Angela; Smith, Bettye; Stucky, Galen (1997). "Does abalone nacre form by heteroepitaxial nucleation or by growth through mineral bridges?". Chemistry of Materials 9 (8): 1731–1740.  
  14. ^ Checa, Antonio; Cartwright, Julyan; Willinger, Marc-Georg (2011). "Mineral bridges in nacre". Journal of Structural Biology 176 (3): 330–339.  
  15. ^ Bruce Runnegar & S Bengtson. "1.4". Origin of Hard Parts — Early Skeletal Fossils (PDF). 
  16. ^ Buckhorn Lagerstätte of Oklahoma Click on photo for more information.
  17. ^ Jessica Hodin, "Contraband Chic: Mother-of-Pearl Items Sell With Export Restrictions", New York Observer, October 20, 2010
  18. ^ Aron, Jacob (24 July 2012). "Artificial mother of pearl follows nature's recipe". New Scientist. 
  19. ^ "Super-tough glass based on mollusk shells". Retrieved 2014-02-13. 


See also

In 2014, researchers used lasers to create an analogue of nacre by engraving networks of wavy 3D "micro-cracks" in glass. When the slides were subjected to an impact, the micro-cracks absorbed and dispersed the energy, keeping the glass from shattering. Altogether, treated glass was reportedly 200 times tougher than untreated glass.[19]

In 2012, researchers created calcium-based nacre in the laboratory by mimicking its natural growth process.[18]

Manufactured nacre

Mother of pearl is sometimes used to make spoon-like utensils for caviar, so as to not spoil the taste with metallic spoons.


Nacre inlay is often used for music keys and other decorative motifs on musical instruments. Many accordion and concertina bodies are completely covered in nacre, and some guitars have fingerboard or headstock inlays made of nacre (as well as some guitars having plastic inlays designed to imitate the appearance of nacre). The bouzouki and baglamas (Greek plucked string instruments of the lute family) typically feature nacre decorations, as does the related Middle Eastern oud (typically around the sound holes and on the back of the instrument). Bows of stringed instruments such as the violin and cello often have mother of pearl inlay at the frog. It is traditionally used in the valve buttons of trumpets and other brass instruments as well.

Musical instruments

Nacre is also used to decorate watches, knives, guns and jewellery.

Mother of pearl buttons are used in clothing either for functional or decorative purposes. The Pearly Kings and Queens are an elaborate example of this.

Nacre bracelet


Instead of using a marble or tile base, the nacre tesserae can be glued to fiberglass. The result is a lightweight material that offers a seamless installation and there is no limit to the sheet size. Nacre sheets may be used on interior floors, exterior and interior walls, countertops, doors and ceilings. Insertion into architectural elements, such as columns or furniture is easily accomplished.

Both black and white nacre are used for architectural purposes. The natural nacre may be artificially tinted to almost any color. Nacre tesserae may be cut into shapes and laminated to a ceramic tile or marble base. The tesserae are hand-placed and closely sandwiched together, creating an irregular mosaic or pattern (such as a weave). The laminated material is typically about 2 millimetres (0.079 in) thick. The tesserae are then lacquered and polished creating a durable and glossy surface.

White nacre mosaic tiles in the ceiling of the Criterion Restaurant in London


Decorative uses

Widely used for pearl buttons especially during the 1900s, were the shells of the great green turban snail Turbo marmoratus and the large top snail, Tectus niloticus. The international trade in mother of pearl is governed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora, an agreement signed by more than 170 countries.[17]

The main commercial sources of mother of pearl have been the pearl oyster, freshwater pearl mussels, and to a lesser extent the abalone, popular for their sturdiness and beauty in the latter half of the 19th century.

Commercial sources

The form of nacre varies from group to group. In bivalves, the nacre layer is formed of single crystals in a hexagonal close packing. In gastropods, crystals are twinned, and in cephalopods, they are pseudohexagonal monocrystals, which are often twinned.[6]

In different mollusc groups

Nacre is secreted by the epithelial cells of the mantle tissue of various molluscs. The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as mother of pearl. The layers of nacre smooth the shell surface and help defend the soft tissues against parasites and damaging debris by entombing them in successive layers of nacre, forming either a blister pearl attached to the interior of the shell, or a free pearl within the mantle tissues. The process is called encystation and it continues as long as the mollusc lives.

Fossil nautiloid shell with original iridescent nacre in fossiliferous asphaltic limestone, Oklahoma. Dated to the late Middle Pennsylvanian, which makes it - by far - the oldest deposit in the world with aragonitic nacreous shelly fossils.[16]


Nacre formation is not fully understood. Formation may be mediated by the organic matrix, controlling the onset, duration and form of crystal growth.[11] Individual aragonite "bricks" are believed to quickly grow to the full height of the nacreous layer, and expand until they abut adjacent bricks.[6] This produces the hexagonal close-packing characteristic of nacre.[6] Bricks may nucleate on randomly dispersed elements within the organic layer,[12] well-defined arrangements of proteins,[2] or may grow epitaxially from mineral bridges extending from the underlying tablet.[13][14] Nacre differs from fibrous aragonite – a brittle mineral of the same form – in that the growth in the c-axis (i.e., approximately perpendicular to the shell, in nacre) is slow in nacre, and fast in fibrous aragonite.[15]