dolostone

Dolostone is a carbonate sedimentary rock whose principal mineral is dolomite, the calcium-magnesium carbonate mineral CaMg(CO3)2. In many descriptions, dolostone contains more than 50 percent dolomite by mineral content, with interlayering or inclusions of calcite and other minerals.

Formation can occur in two main ways. Primary dolostone precipitates directly as dolomite during sedimentation when magnesium-rich seawater or groundwater interacts with carbonate sediments. More commonly, limestone undergoes secondary dolomitization during burial diagenesis, when magnesium-rich fluids replace calcium in the calcite lattice to form dolomite.

Texture and structure vary; dolostone can be massive or laminated and often contains nodular, vuggy, or oolitic textures. A well-known diagenetic variety is saddle dolomite, which forms at elevated burial temperatures and pressures during diagenesis.

Occurrence and significance: Dolostone is found in many continents and in numerous sedimentary basins, often in rocks dating from the Cambrian to the Paleozoic, though it persists in younger units as well. It is frequently associated with evaporite sequences and reefal carbonates. Dolostone can act as a reservoir rock for hydrocarbons when secondary porosity and permeability are enhanced by dissolution and dolomitization; however, dolomitization can also reduce porosity in some settings.

Relation to limestone: Limestone is primarily calcite (CaCO3). Dolostone forms when a portion of the calcite is transformed to dolomite via magnesium enrichment; many deposits contain both minerals.

Economic uses: Dolostone is quarried as dimension stone and as a source of magnesium; it also serves as crushed stone for construction, and some varieties are used ornamentally.