Mineralogy, Raman spectroscopy and lattice parameter characterization of biotite with hexagonal structure from Borujerd hornfels and migmatites

Biotite is a common rock-forming mineral and accepts a variety of elements in its structure. The valuable information of crystallization conditions of the biotite mineral obtain on natural biotite composition. The biotite mineral is one of the main mineral phases of pelitic rocks which are formed in a wide range of geological conditions. In this research, microscopic mineralogy, Raman spectroscopy, and X-ray diffraction of biotite minerals from hornfels and migmatites from the Borujerd granitoid aureole in the Sanandaj Sirjan zone investigated. On microscopic studies, mica crystals display common biotite characterizations but the mineral is uniaxial not biaxial as ordinary mica with a monoclinic system. Based on X-ray diffraction, the biotite crystals form in hexagonal crystalline habit. The Raman spectroscopy also reveals the variations in number and shifts on peaks in the range of 500 to 750 cm-1. Based on XRD data, the unit cell lattice parameters have revealed hexagonal mica crystals for the Borujerd migmatite and hornfels. Previous works reported temperatures in the range of 642 to 750 C° for the studied rocks. Investigation on synthetic biotite mineral suggests temperature above 700 C° for monoclinic to hexagonal transformation which confirm the formation of the high-temperature metamorphic event in the Borujerd region.