On the difference between marble, limestone and dolomite and their protection methods

There is a common problem in the stone industry: sometimes a specific stone looks "not worthy of its name". The differences and differences between marble, limestone and dolomite may only be distinguished to a large extent by professionals. For most building owners, they only pay attention to the appearance of stone, and they may not care about which kind of stone is used.

However, in many cases, it is very important to distinguish these kinds of natural stones. At least for the end users, understanding the differences of these seemingly identical stones will help them to make a comprehensive comparison when they purchase.

Let's learn more about the characteristics of marble, limestone and dolomite.

Marble

Marble is also called metamorphic or recrystallized limestone. The real marble is a kind of calcite metamorphic rock with crystal structure. Marble is derived from limestone according to the metamorphism of regional stone. Generally, it contains large and rough crystals, of which calcite accounts for more than 99%. The crystal can be seen by naked eyes, especially on its cross section.

The pore density of most typical limestone is less than 1%, compared with marble, the density is much higher. Because of its crystal structure, many marbles are translucent, with a visible thickness of more than 30 cm, while non crystalline limestone is opaque. Due to the different origin and internal composition of marble, the color of natural stone is different.

In the construction industry, people usually refer to a variety of stone materials, including limestone, dolomite and serpentine. According to the American marble Association, all rocks with natural calcareous and polished brightness for commercial use are called marble, including dolomite and serpentine.

limeston

Limestone is also called calcite and calcium carbonate. Its MOH is 3.

Limestone is a kind of rock with a single calcite mineral composition, accounting for 95% of calcite, and contains a small amount of minerals including dolomite, siderite, quartz, feldspar, mica and clay minerals that can reflect the color of stone. The pure limestone is white. Limonite and siderite make limestone produce yellow brown patterns and colors, such as blood red, sea green, chlorite green, asphalt gray and black.

Limestone produced in seawater is composed of bone fragments of animals and plants, physical changes of calcareous mud and organic matters in seawater. After the organic matter died, the carbonate was dissolved in the sea water, accumulated in the sea floor, and gradually formed calcium carbonate and shell texture. Generally, after limestone is cut, it will be found that there are intact or damaged biological fossils inside the stone.

Unless limestone forms a reef, generally speaking, limestone from the sea has a layered structure. The structure may be dense or granular.

dolomite

The main component of dolomite is magnesium calcium carbonate with MOH between 3.5 and 4.

The main components of dolomite are calcium carbonate and magnesium carbonate. This kind of stone looks very close to limestone in appearance. In fact, dolomite is often found in areas where limestone deposits are found. Most dolomite deposits contain a certain proportion of limestone. The important basis for distinguishing dolomite is that the content of dolomite mineral in the rock is not less than 50%. In addition, dolomite is porous stone. Because the chemical composition of dolomite is not sensitive to acid, dolomite has better weather resistance.

Generally speaking, people usually use hardness test and acid test to distinguish limestone and dolomite.

MOH is a simple mechanical test method, which uses another metal with known hardness to scratch the stone. The hardness of dolomite is between 3 and 4. The acid test method is to apply diluted hydrochloric acid to the surface of stone. The reaction of limestone is strong, while that of dolomite is not obvious, and the surface will form powder. If the above test results are not obvious, laboratory analysis is needed. If you can know the source of the stone, the mineral types and composition will be clear.

Generally speaking, marble, limestone and dolomite can be used alternately as building materials. But even if they belong to the same category, their physical properties are different. Before deciding which kind of stone is most suitable for use, all factors such as absorptivity, density and structural integrity of stone should be taken into account. We can learn from the use of stone materials in other buildings. For example, the exterior wall of a building with a history of 100 years can be used as a reference for our exterior wall engineering.

Limestone has a strong absorptivity. In view of this feature, when laying the ground with limestone and other areas, we should take into account the pollution that is likely to occur in the future, such as scribbling and scribbling. Stone materials with high density and low absorptivity shall be used in the areas susceptible to environmental damage and heavy pressure

From the perspective of historical buildings, dolomite has been used as the exterior wall surface, and its ability to withstand weathering or erosion is stronger than marble and limestone. Because of its low content of calcite, it has strong weather resistance to air pollution (mainly acid).

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