Auxeticity of Calcium Carbonate CaCO3 is explored for the polymorphs commonly known as calcite, which is trigonal, and aragonite, which is orthorhombic. A decomposition of the compliance tensor is presented for the trigonal and orthorhombic classes that simplifies the analysis of extreme values of Lamé compliance and Poisson's ratio. Simple criteria for the determination of auxeticity are proposed and discussed for a wide variety of trigonal and orthorhombic crystals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

With the aim of exploring extreme elastic properties, decompositions of the compliance tensor are established for various crystal classes. Representations are deduced that lead directly to well-structured forms for analyzing extreme properties. The properties of primary interest are the Lamé compliance and the axial compliance (reciprocal Young’s modulus). These exteme values and the corresponding directions play significant role in the study of those for the Poisson’s ratio, in particular the search for a negative minimum.

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