The CaO content is a key indicator for evaluating the grade of limestone deposits. Generally, the activity of lime is positively correlated with CaO content; as CaO content rises, the activity index increases accordingly. When CaO content ≤ 52%, its specific surface area drops significantly. Lime used for adsorption and removal applications (metallurgical desulfurizers, hazardous waste disinfectants, etc.) must feature high specific surface area and high micropore specific surface area, which requires limestone raw materials to have a high CaO content. Geographically, northern Chinese limestone with CaO content above 53% and southern Chinese limestone with CaO content above 54% possess prominent advantages for developing high-value-added product chains such as nano calcium carbonate and ultra-fine ground calcium carbonate.

During limestone calcination, CaO reacts with Fe₂O₃ at 800–900 °C to generate large amounts of low-melting calcium ferrite salts. This not only reduces lime activity but also causes lime adhesion. In the presence of CO during calcination, CO acts as a reducing agent to convert Fe₂O₃ into fusible FeO, which further reacts with CaO to form fusible compounds and trigger lime ring formation. In the metallurgical industry, especially steelmaking, limestone serves as a flux, imposing strict limits on iron oxide content. Normally, Fe₂O₃ content in limestone for steel mills should be below 4% to guarantee favorable reactivity and stability at high temperatures. In the production of light calcium carbonate and nano calcium carbonate, iron mainly exists as Fe³⁺ in calcium carbonate, the primary cause of reduced whiteness. Limestone for high-value-added light calcium carbonate production requires Fe₂O₃ ≤ 0.5%, while that for nano calcium carbonate requires Fe₂O₃ ≤ 0.1%.

During limestone calcination, CaO reacts with Al₂O₃ at 500–900 °C to produce substantial low-melting tricalcium aluminate (3CaO·Al₂O₃). Such low-melting phases drastically lower lime activity. In addition, formed CaO·Fe₂O₃ can participate in reactions to finally generate tetracalcium aluminoferrite (4CaO·Al₂O₃·Fe₂O₃). Abundant low-melting compounds during calcination readily form large liquid phases, resulting in lime adhesion and ring formation. This severely disturbs kiln operation and shortens the service life of kilns and refractory materials. In the building materials industry, Al₂O₃ content in limestone is generally specified below 2.0%. For manufacturing high-value-added calcium products, the allowable Al₂O₃ impurity content is no higher than 0.4%.

Magnesium oxide (MgO) is one of the common major impurities in limestone deposits. Excessively high MgO content enables high-magnesium limestone to start endothermic decomposition in the preheating zone of calcination kilns, leading to insufficient raw meal preheating and delayed calcium carbonate decomposition. This wastes fuel heat and markedly increases underburning rate. In cement clinker, the maximum solid-soluted MgO content is approximately 2%, and the remainder exists as free periclase. Periclase hydrates slowly with volume expansion during hydration, which causes poor cement soundness. The building materials industry generally limits MgO content in cement clinker to no more than 5.0%; the metallurgical industry requires MgO content in metallurgical lime not to exceed 1.5%. Limestone for light calcium carbonate production usually demands MgO impurity content < 0.7%, whereas that for nano calcium carbonate requires MgO < 0.4%.

High SiO₂ content in limestone raw materials leads to high abrasiveness and poor grindability, causing severe wear to equipment and silo linings. Higher SiO₂ impurity content makes calcination more difficult, and increases calcium silicate inclusions in calcined clinker, further deteriorating raw meal burnability. Generally, limestone for cement clinker production requires w(SiO₂) ＜ 4.0%. For manufacturing high-value-added products including light calcium carbonate and nano calcium carbonate, SiO₂ impurity content in limestone shall not exceed 1%.