The crystal structure, micro morphology, and surface functional groups of chambersite from Jixian, Tianjin Province (China), were studied during the process of heating. In situ high-temperature X-ray diffraction, conventional X-ray diffraction, thermal analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to determine the effects of different heating temperatures on the structure, morphology, and composition of the samples. The results showed that chambersite phase transformation from the orthorhombic system to the cubic system occurred at 408–410 °C. At 900 °C chambersite was partially decomposed to form new crystals such as manganese metaborate [Mn(BO2)2] and iron oxoborate (Fe3BO6); the manganese metaborate further decomposed into manganese oxide and boric acid at 1000 °C. Chambersite generated a large number of columnar crystals at 900 °C. The recrystallization of chambersite was facilitated by a furnace-controlled cooling process at 900–1050 °C, allowing sufficient energy and time. The present study reflects the thermal reaction of chambersite, which could be applied in microwave absorbing and neutron shielding ceramic materials.