[Crystal chemistry of two cases of subdeltoid calcification]

We studied the mineral phase of two cases of subdeltoid calcification by thermogravimetry, infrared spectometry and X ray diffraction. We have shown that these were phosphates deficient in calcium ions with an apatite structure. They contained both carbonate ions and HPO4 ions in variable proportions from one sample to another. These phosphates are very similar both by their structure and their composition to phosphates in bony tissue. They differ by the fact that they are better crystallised than the latter.