Dolomite

When limestone contains small amounts of the dolomite mineral it is known as dolomitic limestone whereas in the past it was called magnesian limestone. The name dolomite is also used when describing the sedimentary carbonate rock dolostone because it is primarily composed of the mineral dolomite.

The dolomite mineral, when crystalised, forms pink to grey or white crystals. Small amounts of iron give dolomite mineral crystals a yellow to brown tint. A high manganese content gives the crystals a pink-rosey colour. Crystal twinning is commonplace, a phenomenon that takes place when two separate crystal share the same lattice points in a symmetrical manner. It is a double carbonate, meaning it has a different crystal structuring arrangement and does not easily dissolve or 'fizz' in dilute hydrochloric acid.

Dolomite has the following attributes:
- Once processed it is used in the production of float glass
- Useful as a flux in the smelting of steel and iron
- The host rock for base metals such as copper, zinc and lead ore deposits
- Acts as a reservoir rock in containing petroleum
- A rich source of magnesium oxide
- A concrete aggregate
- An ornamental stone
- A soil enhancer

Dolomite is used widely in the horticulture industry as when added to soils it acts as a pH buffer with particular usefulness in this area for home or container gardening use. It is also used for the same reason in salt-water aquariums where it helps buffer changes to the pH of the water. Dolomite is also able to insulate against cosmic rays. The main difference between lime sand and dolomite is that dolomite contains calcium and magnesium. This makes dolomite a most effective neutralising agent.

Limestone type rock produces the most useful and best quality dolomite and all it requires to make it a commercial product is for it to be crushed and screened, preferable to less than 3mm. Ideally commercial grade dolomite should have a talc like appearance of a pinkish white colouring and have a low sodium content. Much of the dolomite produced in Western Australia is derived from dry salt lake beds. This means it has a high sodium content which lowers its neutralising attributes. It is also clay based and turns into a slurry when it comes into contact with water.

Most farmers buy dolomite to alter the pH of their soils as it contains potassium, sodium, magnesium and calcium, all the necessary elements to influence soil pH levels.

South Australia is the largest producer of industrial grade dolomite in Australia, producing around 1.1 million tonnes each year. Australia’s largest dolomite mining operation is in South Australia at Ardrossan on the Yorke Peninsula. It is owned by OneSteel and has its own crushing plant and ship loading facility. The dolomite produced at Ardrossan is fine grained, brown to yellow in colour and quite dense. Lump ore is sold to the steel-making industry at Whyalla, Newcastle and Port Kembla where it is used as a flux. It is also used as a refractory product at the Whyalla steelworks. Twenty five percent of OneSteel's dolomite production is exported to Japan.