Sepiolite deposits have been recently discovered in northeastern Iran. However, there is still little information about its physicochemical and mineralogical characteristics. Therefore, the collapse of the sepiolite (with sizes of < 63 μm) structure induced by temperature elevation in an electric furnace at 350, 550, and 850 °C for 4 hours was studied using X-ray diffraction (XRD) in combination with Thermogravimetric analysis (TGA) and infrared spectroscopic analysis. Results showed that the main mineral constituent of the samples is a well crystallized sepiolite. However, dolomite and quartz were also present in minor amounts. Results also revealed that with temperature different phases including ‘sepiolite dihydrite’, ‘sepiolite anhydrite’ and ‘enstatite’ were formed, as magnesium coordinated water and octahedrically coordinated hydroxyl groups, were eliminated and the dehydroxylated phase was recrystallized to enstatite, a stable form of magnesium silicate (MgSiO3).