Abstract
In the course of the crystal analyses of autunite and xanthophyllite several common crystallographical properties, in particular, constancy of reciprocal main axes observed across the stage of crystal transition were found. Similar character were also observed in silicate minerals such as quartz, feldspars and pyroxenes, and in sulfide minerals such as digenite and sphalerite.
Writers discusscd also the relation between twinning axis and reciprocal main axis, and proposed to introduce a conception of reciprocal lattice for clear and accurate descriptions of twinning, especially for those of monoclinic or triclinic crystals.
