C. Giacobbe and D. , Catherine Dejoie for their assistance during beam time We particularly acknowledge Dr Andrew Fitch, scientist in charge of ID22 at ESRF, for his help and advices in X-ray diffraction measurements. One of us (EZ) thanks the Shore Fund in Advanced Composites (Technion) for partial financial support, ) Weiner, S.; Addadi, L., Design strategies in mineralized biological materials. J. Mater, 1989.

C. Addadi, L. Weiner, S. Espinosa, H. D. Rim, J. E. Barthelat et al., Biomineralization: mineral formation by organisms Biological materials: Structure and mechanical properties Merger of structure and material in nacre and bone -Perspectives on de novo biomimetic materials Architectured materials in engineering and biology: fabrication, structure, mechanics and performance, Annual Reviews: Palo Alto Calcitic microlenses as part of the photoreceptor system in brittlestars, pp.689-702, 1997.

B. M. Heatfield and B. A. Smith, Growth of the calcareous skeleton during regeneration of spines of the sea urchin,strongylocentrotus purpuratus (stimpson): A light and scanning electron microscopic study, Journal of Morphology, vol.23, issue.1, pp.57-90, 1971.
DOI : 10.1016/B978-1-4832-3241-6.50013-5

U. Magdans and H. Gies, Single crystal structure analysis of sea urchin spine calcites: Systematic investigations of the Ca/Mg distribution as a function of habitat of the sea urchin and the sample location in the spine, European Journal of Mineralogy, vol.16, issue.2, pp.16-261, 2004.
DOI : 10.1127/0935-1221/2004/0016-0261

L. Addadi, S. Weiner, and Y. Politi, Differences between Bond Lengths in Biogenic and Geological Calcite, Cryst. Growth Des, vol.10, issue.3, pp.1207-1214, 2010.
URL : https://hal.archives-ouvertes.fr/hal-00465524

S. Weiner and L. Addadi, Role of Magnesium Ion in the Stabilization of Biogenic Amorphous Calcium Carbonate: A Structure-Function Investigation, Chem. Mat, issue.1, pp.22-161, 2010.

J. Weber, R. Greer, B. Voight, E. White, and R. Roy, Unusual strength properties of echinoderm calcite related to structure, Journal of Ultrastructure Research, vol.26, issue.5-6, pp.5-6, 1969.
DOI : 10.1016/S0022-5320(69)90043-4

L. Addadi, P. Gilbert, and S. Weiner, The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution, Proc. Natl. Acad. Sci. U. S. A, issue.15, pp.106-6048, 2009.

A. Veis, Organic Matrix-related mineralization of sea urchin spicules, spines, test and teeth, Frontiers in Bioscience, vol.16, issue.1, pp.2540-2560, 2011.
DOI : 10.2741/3871

P. Gorzelak, J. Stolarski, P. Dubois, C. Kopp, and A. Meibom, (26)mg labeling of the sea urchin regenerating spine: Insights into echinoderm biomineralization process, J. Struct. Biol, issue.181, pp.176-119, 2011.

C. Moureaux, A. Perez-huerta, P. Compere, W. Zhu, T. Leloup et al., Structure, composition and mechanical relations to function in sea urchin spine, Journal of Structural Biology, vol.170, issue.1, pp.170-211, 2010.
DOI : 10.1016/j.jsb.2010.01.003

S. Weiner, Organic matrix-like macromolecules associated with the mineral phase of sea-urchin skeletal plates and teeth, J. Exp. Zool, issue.1, pp.234-241, 1985.

S. Albeck, J. Aizenberg, L. Addadi, and S. Weiner, Interactions of various skeletal intracrystalline components with calcite crystals, Journal of the American Chemical Society, vol.115, issue.25, pp.115-11691, 1993.
DOI : 10.1021/ja00078a005

F. Brummer and F. Marin, Spine and test skeletal matrices of the Mediterranean sea urchin Arbacia lixula -a comparative characterization of their sugar signature, Febs J, vol.2015, issue.10, pp.282-1891
URL : https://hal.archives-ouvertes.fr/hal-01154626

J. Aizenberg, J. Hanson, T. F. Koetzle, S. Weiner, and L. Addadi, Control of Macromolecule Distribution within Synthetic and Biogenic Single Calcite Crystals, Journal of the American Chemical Society, vol.119, issue.5, pp.119-881, 1997.
DOI : 10.1021/ja9628821

L. Ameye, G. De-becker, C. Killian, F. Wilt, R. Kemps et al., Proteins and Saccharides of the Sea Urchin Organic Matrix of Mineralization: Characterization and Localization in the Spine Skeleton, Journal of Structural Biology, vol.134, issue.1, pp.134-56, 2001.
DOI : 10.1006/jsbi.2001.4361

T. W. Goodwin and S. Srisukh, A study of the pigments of the sea-urchins, echinusesculentus l and paracentrotus-lividus lamarck, Biochem. J, issue.1, pp.47-69, 1950.

G. Donnay and D. L. Pawson, X-ray Diffraction Studies of Echinoderm Plates, Science, vol.166, issue.3909, pp.1147-1150, 1969.
DOI : 10.1126/science.166.3909.1147

K. M. Towe, Echinoderm Calcite: Single Crystal or Polycrystalline Aggregate, Science, vol.157, issue.3792, pp.1048-1050, 1967.
DOI : 10.1126/science.157.3792.1048

). Neill and P. L. , Polycrystalline Echinoderm Calcite and Its Fracture Mechanics, Science, vol.213, issue.4508, pp.646-648, 1981.
DOI : 10.1126/science.213.4508.646

A. Berman, L. Addadi, and S. Weiner, Interactions of sea-urchin skeleton macromolecules with growing calcite crystals -a study of intracrystalline proteins, Nature, issue.6156, pp.331-546, 1988.

E. Weber and B. Pokroy, Intracrystalline inclusions within single crystalline hosts: from biomineralization to bio-inspired crystal growth, CrystEngComm, vol.26, issue.3, pp.5873-5883, 2015.
DOI : 10.1021/la100049s
URL : http://arxiv.org/pdf/1609.05463

J. Aizenberg, J. Hanson, T. F. Koetzle, L. Leiserowitz, S. Weiner et al., Biologically Induced Reduction in Symmetry: A Study of Crystal Texture of Calcitic Sponge Spicules, Chemistry - A European Journal, vol.1, issue.7, pp.414-422, 1995.
DOI : 10.1107/S0108768185002245

B. Pokroy, A. N. Fitch, F. Marin, M. Kapon, N. Adir et al., Anisotropic lattice distortions in biogenic calcite induced by intra-crystalline organic molecules, Journal of Structural Biology, vol.155, issue.1, pp.155-96, 2006.
DOI : 10.1016/j.jsb.2006.03.008
URL : https://hal.archives-ouvertes.fr/hal-00198280

P. Fratzl, Nanostructure of Biogenic Calcite and Its Modification under Annealing: Study by High-Resolution X-ray Diffraction and Nanoindentation. Cryst. Growth Des, pp.14-5275, 2014.

C. Gilow, E. Zolotoyabko, O. Paris, P. Fratzl, and B. Aichmayer, Nanostructure of Biogenic Calcite Crystals: A View by Small-Angle X-Ray Scattering, Crystal Growth & Design, vol.11, issue.6, pp.2054-2058, 2011.
DOI : 10.1021/cg200136t

D. M. Raup, Crystallography of Echinoid Calcite, The Journal of Geology, vol.67, issue.6, pp.661-674, 1959.
DOI : 10.1086/626624

E. Zolotoyabko and B. Pokroy, Biomineralization of calcium carbonate: structural aspects, CrystEngComm, vol.86, issue.12, pp.1156-1161, 2007.
DOI : 10.2138/am-2001-11-1222

B. Pokroy, J. P. Quintana, E. N. Caspi, A. Berner, and E. Zolotoyabko, Anisotropic lattice distortions in biogenic aragonite, Nature Materials, vol.20, issue.12, pp.900-902, 2004.
DOI : 10.1107/S0021889887087090

E. Zolotoyabko, Anisotropic Lattice Distortions in Biogenic Minerals Originated from Strong Atomic Interactions at Organic/Inorganic Interfaces, Adv. Mater. Interfaces, vol.2017, issue.41, pp.1-12

B. Pokroy, A. N. Fitch, and E. Zolotoyabko, The Microstructure of Biogenic Calcite: A View by High-Resolution Synchrotron Powder Diffraction, Advanced Materials, vol.109, issue.18, pp.18-2363, 2006.
DOI : 10.6028/jres.109.010

L. Addadi, S. Raz, and S. Weiner, Taking advantage of disorder: Amorphous calcium carbonate and its roles in biomineralization, Adv. Mater, issue.12, pp.15-959, 2003.

L. B. Gower, Biomimetic Model Systems for Investigating the Amorphous Precursor Pathway and Its Role in Biomineralization, Chemical Reviews, vol.108, issue.11, pp.4551-4627, 2008.
DOI : 10.1021/cr800443h

S. Weiner and L. Addadi, Crystallization Pathways in Biomineralization, Annual Review of Materials Research, vol.41, issue.1, pp.21-40, 1380.
DOI : 10.1146/annurev-matsci-062910-095803

J. Aizenberg, S. Weiner, and L. Addadi, Coexistence of Amorphous and Crystalline Calcium Carbonate in Skeletal Tissues, Connective Tissue Research, vol.9, issue.1, pp.20-25, 2003.
DOI : 10.1021/ja00078a005

Y. Politi, Y. Levi-kalisman, S. Raz, F. Wilt, L. Addadi et al., Structural Characterization of the Transient Amorphous Calcium Carbonate Precursor Phase in Sea Urchin Embryos, Advanced Functional Materials, vol.117, issue.209, pp.16-1289, 2006.
DOI : 10.1002/adfm.200600134

S. Weiner and P. Gilbert, Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule, Proc. Natl. Acad. Sci. U. S. A, vol.105, issue.4547, pp.17362-17366, 2008.

M. Sztucki, M. Burghammer, S. Maltsev, C. Jager, and H. Colfen, Structure-property relationships of a biological mesocrystal in the adult sea urchin spine, Proc. Natl. Acad. Sci. U. S
URL : https://hal.archives-ouvertes.fr/hal-01391153

Y. Politi, T. Arad, E. Klein, S. Weiner, and L. Addadi, Sea Urchin Spine Calcite Forms via a Transient Amorphous Calcium Carbonate Phase, Science, vol.306, issue.5699, pp.1161-1164, 2004.
DOI : 10.1126/science.1102289

X. Su, S. Kamat, and A. H. Heuer, The structure of sea urchin spines, large biogenic single crystals of calcite, J. Mater. Sci, issue.22, pp.35-5545, 2000.

A. N. Fitch, The high resolution powder diffraction beam line at ESRF, Journal of Research of the National Institute of Standards and Technology, vol.109, issue.1, pp.133-142, 2004.
DOI : 10.6028/jres.109.010
URL : http://doi.org/10.6028/jres.109.010

R. Carvajal, J. Hall, D. L. Bodnar, and R. J. , Recent advances in magnetic-structure determination by neutron powder diffraction Comparison of fluid inclusion decrepitation and acousticemission profiles of westerly granite and sioux quartzite, Physica B Tectonophysics, vol.192, issue.12524, pp.55-69, 1989.

J. E. Lamar and R. S. Shrode, Water soluble salts in limestone and dolomites, Economic Geology, vol.48, issue.2, pp.97-112, 1953.
DOI : 10.2113/gsecongeo.48.2.97

D. Wardecki, R. Przenioslo, and M. Brunelli, Internal pressure in annealed biogenic aragonite, CrystEngComm, vol.86, issue.10, pp.1450-1453, 2008.
DOI : 10.2138/am-2001-11-1222

N. Khan, D. Dollimore, K. Alexander, F. W. Wilburn, S. L. Wolf et al., The origin of the exothermic peak in the thermal decomposition of basic magnesium carbonate Synergy of Mg2+ and poly(aspartic acid) in additive-controlled calcium carbonate precipitation Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate, 57) Radha Proc. Natl. Acad. Sci. U. S. A. 2010, pp.321-333, 2001.

B. Shir, I. Kababya, S. Schmidt, and A. , Molecular-Level Structure-Property Relationships in Biogenic Calcium Carbonates: The Unique Insights of Solid-State NMR Spectroscopy, Isr. J. Chem, pp.541-543, 2014.

L. Bergstrom, C. W. Tai, T. K. Sham, M. Eden, and N. Hedin, Proto-Calcite and Proto-Vaterite in Amorphous Calcium Carbonates, Angew. Chem.-Int. Edit, issue.47, pp.49-8889, 2010.

R. J. Reeder and Y. Tang, Characterization of Structure in Biogenic Amorphous Calcium Carbonate: Pair Distribution Function and Nuclear Magnetic Resonance Studies of Lobster Gastrolith, biomineral in crayfish gastroliths. Proc. Natl, pp.14763-14768, 2011.
DOI : 10.1021/cg301653s

S. Y. Yang, H. H. Chang, C. J. Lin, S. J. Huang, and J. C. Chan, Is Mg-stabilized amorphous calcium carbonate a homogeneous mixture of amorphous magnesium carbonate and amorphous calcium carbonate?, Chemical Communications, vol.323, issue.77, pp.2016-52
DOI : 10.1126/science.1169434

T. W. Tsai and J. C. Chan, Recent Progress in the Solid-State NMR Studies of Biomineralization, In Annual Reports on Nmr Spectroscopy, vol.73, issue.73, pp.1-61, 2011.
DOI : 10.1016/B978-0-08-097074-5.00001-3

A. G. De-la-torre, S. Bruque, and M. A. Aranda, Rietveld quantitative amorphous content analysis, Journal of Applied Crystallography, vol.34, issue.2, pp.196-202, 2001.
DOI : 10.1107/S0021889801002485

N. Floquet, D. Vielzeuf, D. Ferry, A. Ricolleau, V. Heresanu et al., Thermally Induced Modifications and Phase Transformations of Red Coral Mg-Calcite Skeletons from Infrared Spectroscopy and High Resolution Synchrotron Powder Diffraction Analyses, Crystal Growth & Design, vol.15, issue.8, pp.15-3690, 2015.
DOI : 10.1021/acs.cgd.5b00291
URL : https://hal.archives-ouvertes.fr/hal-01215565

C. C. Chen, C. C. Lin, L. G. Liu, S. V. Sinogeikin, and J. D. Bass, Elasticity of singlecrystal calcite and rhodochrosite by Brillouin spectroscopy, Am. Miner, pp.8611-8623, 2001.

J. P. Cuif, Y. Dauphin, P. Berthet, J. Jegoudez, H. Nagasawa et al., Associated water and organic compounds in coral skeletons: Quantitative thermogravimetry coupled to infrared absorption spectrometry Microstructural Variation of Biogenic Calcite with Intracrystalline Organic Macromolecules, Geochem. Geophys. Geosyst, vol.5, issue.691, pp.1-9, 2004.

S. Weiner and L. Hood, Soluble protein of the organic matrix of mollusk shells: a potential template for shell formation, Science, vol.1, issue.3482, pp.987-989, 0190.
DOI : 10.1021/bi00910a024

F. Marin, G. Luquet, B. Marie, and D. Medakovic, Molluscan Shell Proteins: Primary Structure, Origin, and Evolution, In Current Topics in Developmental Biology, vol.80, pp.209-276, 2008.
DOI : 10.1016/S0070-2153(07)80006-8
URL : https://hal.archives-ouvertes.fr/hal-00197133

G. Alcaraz, C. Riondet, and P. Westbroek, Caspartin and calprismin, two proteins of the shell calcitic prisms of the Mediterranean fan mussel Pinna nobilis, J. Biol. Chem, issue.40, pp.280-33895, 2005.
URL : https://hal.archives-ouvertes.fr/inserm-00166083

J. F. Nye, Y. Politi, and J. C. Weaver, Physical Properties of Crystals Built for tough conditions, Science, issue.746223, pp.347-712, 2001.