Effects of CaO and MgO on the Crystallization Behavior of Basalt Melt

Basalt fiber, an innovative inorganic, high-performance material, is valued for its environmental friendliness and excellent properties. However, compositional variations in basalt can induce crystallization during the cooling process, which significantly affects fiber production. This study systematically investigated phase transitions in basalt melt during cooling, with special attention to the effects of CaO and MgO concentrations. Through a combination of analytical techniques, including X-ray diffraction, differential scanning calorimetry, and Fourier-transform infrared spectroscopy, we examined the influence of CaO and MgO on basalt melt crystallization behavior. During cooling, the basalt melt underwent sequential crystallization, with plagioclase forming first, followed by clinopyroxene, and finally hematite and spinel. Although increased CaO content inhibited the formation of hematite and spinel, it strongly promoted the crystallization of clinopyroxene and plagioclase, leading to an overall enhancement in crystallization tendency. In contrast, moderate MgO addition (up to 4 wt.%) suppressed mineral crystallization, whereas higher MgO content (> 4 wt.%) promoted the crystallization of clinopyroxene and orthopyroxene, resulting in an initial decrease followed by an increase in overall crystallinity. Both CaO and MgO were found to disrupt the glass network structure.