Siliceous dolostone from the Middle Proterozoic Jixian System is broadly distributed in the Ordos basin and adjacent areas. Although silica is well- known as the principal factor tightening the dolostone, less attention has been paid to its various characteristics and the relationships between mineral phases. This lack of understanding has hindered the rational interpretation of the silicification and densification mechanisms of these rocks. Field observations, along with petrological and geochemical studies, reveal three distinct forms of silica within the dolostone: layered/banded, nodular/agglomerated, and dispersed. Layered and banded silica formations involve large- scale amalgamation of silica and dolostone. Microscopically, these formations consist of cryptocrystalline/microcrystalline quartz, with low rare earth element content, faint negative Ce anomalies, subtle positive Eu anomalies, and elevated Al2O3 and TiO2 content. They originate from direct silica precipitation in shallow continental margin waters, facilitated by oxygen- rich, photosynthetic cyanobacteria induced by marine microorganisms. Nodular/agglomerated silica has an irregular spatial distribution within the bedrock matrix. It is predominantly composed of chalcedony and microcrystalline quartz. The LaN/CeN ratio approximates unity, accompanied by subtle negative anomalies in Ce and Eu. These entities form during late diagenesis through silica infusion from seawater and terrestrial detritus, filling voids such as mold and framework cavities. Dispersed silica lacks distinctive structural attributes. Under microscopic observation, it is mainly composed of cryptocrystalline/microcrystalline quartz. Importantly, it presents a conspicuous and elevated positive Eu anomaly, resulting from the metasomatic replacement of dolomite with silica. The silicification in the Jixian System dolostone displays selective, cyclical patterns, resulting in compaction and reduced rock porosity. However, these processes do not contribute positively to the formation of high- grade reservoirs.