Structural characterisation of X-ray amorphous calcium carbonate (ACC) in sternal deposits of the crustacea Porcellio scaber

Mineral deposits in land-based woodlice (crustacea, Porcellio scaber) were analysed by high-resolution X-ray diffraction, X-ray absorption spectroscopy (EXAFS) and infrared microscopy. Calcium carbonate is stored within the first four anterior sternites before changing the cuticle (shell). These deposits consist of fully X-ray amorphous calcium carbonate (primary particle size less than 100 A). The short-range order is comparable to crystalline calcium carbonate phases (first coordination shell), but there is increasing structural disorder beyond about 3 A. This high degree of structural disorder gives a high solubility, i.e. an easy mobilisation within the biological system. The results are compared with EXAFS data from the literature on other biogenic amorphous calcium carbonates.