The upper limit of crystallization temperature (T_c) of basalt melt is crucial for the production of continuous basalt fibers (CBFs). However, the precisely measuring T_c for basalt systems has been a challenging and time-consuming task. As a result, there is often a mismatch between the fiber-drawing temperature (T_d) and the T_c of basalt melt during CBF production, which hinders the improvement of the mechanical properties and leads to the fiber fracture. To address these limitations, a new approach has been proposed to determine T_c by analyzing the inflection point of the viscosity-temperature curve, This is achieved by fitting an exponential function (y = y₀ + A*exp(R₀*x)). The results of this viscosity fitting technique were compared to the microstructure and morphology of basalt melts quenched at different temperatures, which were assessed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The findings indicate that the results from XRD and micro-observations are in agreement with the viscosity fitting method. Furthermore, the variations of T_c and T_d in binary basalt systems were quantified, and it was revealed that their behavior follows the linear superposition principle based on the mass percentage W_i (i = 1, 2) of the two end members. Empirical formulas have been developed to describe this relationship, which are given as T_cW₁ × T_c1 + W₂ × T _c1 and T_d = W₁ × T_d1 + W₂ × T_d2. These findings not only contribute to the precise measurement of T_c but also provide new insights for modeling the prediction formula of T_c for binary basalt systems.