Abstract

• In the marble of the Mogok Metamorphic Belt from Bawlonelay area, Mogok Township, pyrites crystals exhibit a wide range of different morphologies during regional metamorphism. The pyrite crystals are commonly found as cube, octahedra and cubo-octahedra, pyritohedra and cubopyritohedra habits in the research area. On the basis of pyrite crystal habits, they could form under the different temperature condition which controls the speed at which the crystal grew. Moreover, these pyrite crystals are found in association with ruby in the marble from Bawlonelay. Blue corundum (sapphire) is not associated with ruby in the primary gemstone-bearing bands indicates that available Ti may have been used up in forming sphene (titanite) which is a common associated mineral in these bands. There has no more Ti available to form blue sapphire. The present study would like to consider the hypothesis is that ruby in the marble from Bawlonelay together with pyrite indicate that the original limestone contain impurities of aluminous and iron rich materials. Although there has enough alumina from the intruded igneous rocks (i.e syenite), the element, Fe, that would be formed for the formation of sapphire were already used up as the crystallization of pyrite which is found in association with ruby in the marble of Bawlonelay and no more excess Fe for the formation of sapphire.