Abstract: Direct preparation of glass-ceramics from slag is an efficient way to use the “slag” and “heat” of the slag, making this preparation a sought-after research topic. To prepare glass-ceramics using the Petrurgic method, this paper used silico–manganese slag as the main raw material, along with chromite and serpentine as modifiers. The Petrurgic method is a heat treatment process involving controlled crystallization during slag cooling to form glass-ceramics. The prepared glass-ceramic samples had a diameter of 100 mm and a height of 20 mm. Various tests and analyses such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy with energy dispersive X-ray spectroscopy, flexural strength, compressive strength, water absorption, and bulk density were performed on the samples. The influence of different heat treatment regimens on the phase composition and properties of silico–manganese slag microcrystalline glass was discussed. Additionally, the study investigated the temperature variation inside the glass-ceramic samples, and the results indicated that by modifying the slag and annealing it at 700℃ after cooling to the crystallization temperature, microcrystalline glass meets the performance requirements of natural granite. The temperature range of 900–1050 ℃ was found to be associated with the crystallization of the augite phase, while the temperature range of 1000–1050 ℃ was related to the crystallization of the akermanite phase. With improvements in the heat treatment system, the amount of akermanite phase precipitation will increase, and the grain will become coarser than before. At 900 ℃, the grain growth of the microcrystalline glass was not as significant as that of the samples annealed at 1000 ℃ and 1050 ℃, and the lack of excessive crystallization led to fewer defects inside the glass-ceramics. After studying the temperature profile data, it was observed that during the heat treatment process at 1000–1050 ℃, inconsistent crystallization between the inner and outer parts of the sample resulted in a temperature gradient from the center to the edge. After studying the temperature profile data, it was observed that during the heat treatment process at 1000–1050 ℃, inconsistent crystallization between the inner and outer parts of the sample resulted in a temperature gradient from the center to the edge. However, at 900 ℃, the temperatures of the central and edge regions remained consistent during the crystallization stage. For the heat treatment at 800 ℃, the slag temperature quickly decreased below 900–1050 ℃, making crystallization difficult. The overall trend of the temperature difference between the central and side parts of the sample was similar for all four heat-treatment conditions. After casting the slag into the mold, temperature gradients were formed within the sample. These formations do not affect the types of crystalline phases that precipitate; however, they do affect the quantity of crystallization.