Summary: Besides an attempt to construct a leptonic model of aragonite, the author presents a new method for the determination of the leptonic structure of crystals from their etch-figures.

The structure of aragonite, constructed in such a way that its transformation into that of calcite can be attained with a small expenditure of energy, was tested by means of the method of etch-figures, and a perfect agreement was reached between the figures observed and those deduced. In case of six faces (out of eight observed) the spacings are in perfect agreement with those observed by W. L. Bragg, the remaining two being half of the observed spacings. This discrepancy is explained by a hypothesis (supported by certain facts) that aragonite in its natural occurrence has undergone a partial transformation into calcite.

The structure proposed is unable to explain the intensities of the X-ray spectra. As the knowledge of intensities of X-ray spectra is still very imperfect, this question is not discussed; but it is possible that the cause of this discrepancy may be also sought in the partial transformation of aragonite into calcite.

The constructed leptonic model of aragonite belongs to the space-group C_2h¹, and, therefore, this mineral is monoclinic, and not orthorhombic, as previously thought. This fact, already remarked upon by some mineralogists, places aragonite in the holohedral class of monoclinie system. But as its crystallographic axes are orthorhombic, the monoclinic crystals of aragonite are considered to be pseudo-orthorhombic.