Susan E. Wooley

Gallstone of Unusual Composition: Calcite, Aragonite, and Vaterite

A gallstone of almost perfect octahedral symmetry was composed of a mixture of crystallites of the three polymorphous forms of calcium carbonate: calcite, aragonite, and vaterite.

Phase changes during heating of magnesium ammonium phosphate hexahydrate and magnesium hydrogen phosphate trihydrate to high temperatures

Magnesium ammonium phosphate hexahydrate MgNH4PO4,6H2O and magnesium hydrogen phosphate trihydrate MgHPO4,3H2O have been heated to temperatures up to 1220° and X-ray powder photographs taken of the products. Both substances decompose during the process and gradually change first into an amorphous phase and then into crystalline magnesium pyrophosphate. The incandescence which appears on the ignition of these substances may be associated with the dimerisation of the ion HPO42–.