About crystal morphology of marñasite
Results of marcasite crystals goniometric study from Cambrian clays of Leningrad region are represented. These crystalshave «spear-like» view owing to orthorhrombic bipyramid {111}. As minor forms are noted pinacoids {100} and {010}, prism {130}. The generalization of all literature data leads to the conclusion, that bipyramidal marcasite crystals with the ruling simple form {111} are typical for sediment rocks of initial stage of diagenesis (epigenesis). For hydrothermal marcasite and marcasite of more deep stage of diagenesis (catagenesis) of sediment rocks are typical crystals owing to presence of prismatic faces and (or) pinacoids by various development of their relative sizes. By the assumption, this difference in crystal forms is obliged to relatively low temperatures of marcasite formation in the first case and to relatively high temperatures in the second case.