The arrangement of oxygen atoms in hexagonal rings in crystals of ice and muscovite gives two possible alternatives of epitaxial connection between these two structures. Which one of these two alternatives is favored depends entirely on the location of potassium atoms in the cleavage plane of the muscovite structure. Since potassium atoms are displaced from the normal environment by the slip taking place along partial Burgers vectors, epitaxial growth of ice crystals on muscovite can be used for the determination of the slip directions and hence for the study of partial dislocations in muscovite crystals.