Dolomite

What Does Dolomite Mean?

Dolomite is calcium magnesium carbonate having the chemical formula CaMg(CO₃)₂. It occurs naturally as a mineral and as a rock.

As a mineral, dolomite exists mostly as rhomboidal, sometimes prismatic, translucent or transparent, colorless or white crystals. Small amounts of manganese, iron and other impurities give some dolomite rocks and crystals their color (gray, pink, orange, red, yellow, green or black).

Dolomite may also refer to a sedimentary rock that is at least 90% dolomite. A limestone dolomite consists of 50% to 90% dolomite by weight. The rock is also known as dolomitized limestone because it is thought to originate from limestone that has been transformed into a dolomite by dolomitization. During dolomitization, the calcium in the CaCO₃-rich limestone is partially replaced by magnesium to form dolomite (CaMg(CO₃)₂).

Dolomite rock is also known as dolostone.

In appearance, dolomite looks like the more common calcite (CaCO₃), but as indicated by their chemical formulas, their chemical composition differs. Calcite has no magnesium ions.

In March 1792, Nicolas-Théodore de Saussure named the mineral calcium magnesium carbonate as dolomite after the French mineralogist Deodat de Dolomieu.

Corrosionpedia Explains Dolomite

Among the many uses of dolomite is corrosion prevention, especially for water distribution systems. Dolomite is used in water filters, pipe linings and backfills.

1. Water filter medium

After treatment to make it potable, water is usually soft with a low mineral content and is fairly acidic – the typical characteristics of “corrosive” water. Aside from damage to pipes, corrosion can make water taste bad, cause stains and be toxic.

Small water distribution systems usually use an alkaline media filter or contactor, and a filter bed that includes dolomite through which the water passes to adjust the pH to a level of 7 to 8. Increasing the pH too much is also a problem because highly alkaline water can also be corrosive.

Water that contains the proper amounts of calcium or magnesium salts (to avoid hard water that will form scale) is also less corrosive because the minerals can coat and protect the pipe’s inner walls as well as improve the taste of the water. Dolomite in the filter or contactor is a good source of these minerals because dolomite is dissolved in slightly acidic water as it is filtered.

2. Pipe lining material

Studies have shown that pipe walls with a dolomite coating have the lowest corrosion rate compared to other materials.

3. Bedding and backfill material

Bedding and backfill materials that include dolomite protect underground pipes from corrosion.

Water from desalination or reverse osmosis treatments usually passes through an alkaline media filter that contains dolomite to avoid corrosion and improve taste.