Crystallographic phase determination of calcium sulphate
microcrystals from deep-sea medusae
1
2
2
A. Becker, C. Paulmann , I. Sötje , H. Tiemann , and M. Epple
*
Institute of Inorganic Chemistry, University Duisburg-Essen, D-45117 Essen, Germany
1
HASYLAB at DESY, Notkestr. 85, D-22603 Hamburg, Germany
2
Zoological Institute, University Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany
Inorganic materials are used in many biological systems for different purposes as teeth, bones or
shells. While these mostly consist of calcium carbonate or calcium phosphate, there are also some
examples of calcium sulphate as biomineral [1]. However, in these cases gypsum (calcium sulphate
dihydrate; CaSO42 H2O) is found. This was considered to be the only phase of calcium sulphate
used by nature as biomineral. This assumption was shown to be incorrect by us when we found
calcium sulphate hemihydrate (CaSO40.5 H2O) single crystals in statoliths of the deep sea medusa
Periphylla periphylla (see fig. 1)[2]. This is even more interesting and shows the capabilities of
nature because an organism consisting of 99 % water is able to precipitate a water-deficient
[2]
mineral. Notably, the statoliths are single crystals and not a polycrystalline material . The crystal
structure could be unequivocally determined from diffraction data obtained at the F1 beamline at
HASYLAB.
The results obtained for the statoliths of Periphylla periphylla carried out at beamlines B2 and F1
could lead to consequences in the evolutional theory of medusae because the composition of the
statoliths may serve as taxonomic criterion. Here we studied statoliths of two other species. Initial
results obtained at beamline B2 showed the powder diffraction pattern of calcium sulfate
hemihydrate.
Calcium sulfate hemihydrate crystallizes with channels in the structure that incorporate variable
amounts of crystal water (from 0 to more than 0.5). The hemihydrate CaSO4•0.5 H2O is technically
known as "calcined gypsum" or "plaster of Paris" and heavily used in the construction industry.
Abriel and Nesper surveyed and discussed the structures and resulting symmetries of the calcium
sulphate system intensively[3].
Figure 1: (left) Image of the deep sea medusa Periphylla periphylla. The arrows mark the position
of the statocysts (special organs) which contain the statoliths. These statocysts are supposed to
serve as gravity detectors. (right) Statolith SEM image.
Single crystal diffraction experiment with explanted microcrystals revealed the crystal structure and
give hints on the content of water (which is, however, disordered within the channels).The statoliths
were always single crystals. The small crystal size required the use of the high-intensity
HASYLAB beam line F1.
Up to now three species have been studied at beam line F1, all belonging to the Scyphozoa class
which was formerly believed to have statoliths consisting of gypsum, i.e. the dihydrate. In all cases,
calcium sulphate hemihydrate was found in single crystals. We conclude that the occurrence of this
water-deficient mineral in biology is more widespread than formerly assumed.
References
[1] H.A. Lowenstam, S. Weiner, Oxford University Press, 1989.
[2] H. Tiemann, I. Sötje, G. Jarms, C. Paulmann, M. Epple, B. Hasse, J. Chem. Soc. Dalton Trans.,
1266-1268 (2002).
[3] W. Abriel, R. Nesper, Zeitschrift fuer Kristallographie, 99-113 (1993).