Talking about the difference between marble, limestone and dolomite and their protection methods

Talking about the difference between marble, limestone and dolomite and their protection methods

　　 There is usually such a problem in the stone industry: sometimes a specific stone seems "incorrect". The differences and differences between marble, limestone and dolomite may only be distinguished by professionals to a large extent. For most building owners, they only pay attention to the appearance of the stone, and may not be very concerned about the type of stone used. care.

However, in many cases, it is very important to distinguish between these types of natural stones. At least for end users, understanding the differences between these types of seemingly identical stones will help them to make purchases. Comprehensive comparison.

　　 Let’s take a closer look at the characteristics of marble, limestone and dolomite.

　　 marble

　　Marbleis also called metamorphic or recrystallized limestone. Real marble is a calcite metamorphic rock with a crystal structure. Marble is derived from limestone based on the metamorphism of regional stone, and generally contains large, rough crystals, of which calcite accounts for more than 99%. The crystals are visible to the naked eye, especially on the cross section.

　　 Most typical limestone has a pore density of less than 1%. Compared with marble, the density is much higher. Because of its crystalline structure, many marbles are translucent, generally visible in thickness over 30 cm, while amorphous limestone is opaque. Due to the different origin and internal composition of marble, the color of natural stone varies.

　　 In the construction industry, the marble that people talk about usually refers to a variety of stones including limestone, dolomite and serpentine. The American Marble Association stipulates that all rocks with natural lime quality and brightness that can be polished for commercial use are called marble, including dolomite and serpentine.

　　 limestone

　　 Limestone is also called calcite and calcium carbonate, and its Mohs hardness value (MOH) is 3.

　　 Limestone is a kind of rock that contains a single mineral component of calcite. The calcite component accounts for 95%. The other small amounts of minerals it contains are dolomite, siderite, quartz, feldspar, mica and clay minerals that can reflect the color of the stone. Pure limestone is white. Limonite and siderite cause limestone to produce yellowish-brown patterns and colors, such as blood red, sea green, chlorite green, pitch gray and black.

　　Limestone produced in seawater is composed of bone fragments of animals and plants, physical changes in calcareous mud, and organic matter in seawater. After the death of these organic matter, the carbonate is dissolved in the sea water and accumulated on the bottom of the sea, gradually forming calcium carbonate and shell tissue. Usually, after limestone is cut, there are intact or destroyed biological fossils inside the stone.

　　 Unless limestone forms a reef, in general, limestone produced in the sea has a layered structure. Its structure may be dense, or it may have granular pores.

　　 Dolomite

The main component of 　　 dolomite is calcium magnesium carbonate, and its Mohs hardness value (MOH) is between 3.5 and 4.

　　 Dolomite ore is mainly composed of 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 percentage of limestone. The important basis for distinguishing dolomite is that the content of dolomite minerals in the rock is not less than 50%. In addition, dolomite is a porous stone. Because the chemical composition of dolomite is not sensitive to acidic substances, dolomite has better weather resistance.

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

　　 Mohs Hardness Test (MOH) is a simple mechanical test method that uses another metal of known hardness to scrape the stone. Therefore, the hardness value of dolomite is between 3 and 4. The acid test method is to apply diluted hydrochloric acid to the surface of the stone. The limestone reacts strongly, while the dolomite reaction is not obvious, and the surface will form a powder. If the above test results are not obvious, laboratory analysis is required. If you can know the source of the stone, the type and composition of the mineral will be clear.

　　 Generally speaking, marble, limestone and dolomite can be used alternately as building materials. But even stones belonging to the same category have different physical properties. Before deciding which kind of stone is most suitable for use, all factors such as the absorbency, density and structural integrity of the stone should be considered. Can learn from the use of stone in other buildings. For example, the exterior wall of a 100-year-old building can be used as a reference for our exterior wall engineering.

　　 Limestone is highly absorbent. In view of this feature, when we use limestone to pave the ground and other areas, we should take into account the pollution that may easily occur in the future such as scribbling. In areas susceptible to environmental damage and heavy pressure, use high-density and low-absorbency stone.

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

　　 Generally speaking, marble, dolomite and limestone are all softer stones. Therefore, it is extremely vulnerable to external pollution during construction and future use, exposing its weak points of poor stain resistance, such as being easily polluted by rainwater and dirt. Compared with granite, these three types of stone have higher water permeability and are more susceptible to contamination. To solve this problem, the best way is to protect it.

Nowadays, the permeable protective agent for stone is commonly used internationally. The principle of protection is that the protective agent penetrates into the natural stone, deposits between the tiny particles in the pores of the stone, or attaches to the individual mineral molecules under the surface of the stone. , In order to prevent water, oil and dirt from entering the stone. Permeable protective agents can be water-based and solvent-based, and usually contain silicon, silicone, methyl silicate or other similar silicon compounds. Permeable protective agents can also be divided into two categories: waterproof type and oil-proof type. The waterproof type is mainly used to block water and liquid chemicals, such as fruit drinks, coffee, tea and soda water. The oil-proof permeability protectant is used to prevent water and oil-based liquids from penetrating into the stone, such as edible oil, grease and other oils. Oil-proof penetrating protective agents also have a waterproof function, but waterproof products may not necessarily prevent oily pollution.

　　 When using permeable protective agent for protective treatment, one of the factors that need to be considered is what kind of stone is suitable and where it is laid. In view of the different properties of marble, limestone and dolomite, we should adopt different treatment methods according to the situation. For example, for the daily use of kitchen marble floors, the selected protective agent must have oil-repellent properties. As for the floor of a busy hotel lobby, pedestrians will leave a lot of footprints and it is easy to rub the ground. At this time, in order to protect the gloss of the surface, in addition to treatment with a penetrating protective agent, a layer of surface type should be applied if necessary. The protective agent, even with polishing products for ground polishing.

　　 In addition, another factor to be considered is the maintenance method. If the dolomite or marble floor is scrubbed daily, it is more likely to be damaged by acid chemicals. If the maintenance of the ground is neglected, the dirt will be blocked in the pores of the stone. If the stone itself has high brightness, the gloss may be worn. In this way, no matter how good the protective treatment of the stone surface is, the surface will become dirty and dark. For example, the floor of a busy hotel lobby is regularly dusted and scrubbed with water every day, perhaps only with a surface-type protective agent that can be removed. However, if it is changed to a living room at home, it is not necessary to clean it with a cleaning agent every day. It is enough to use a permeable protective agent with better water resistance for protection.

Finally, it needs to be emphasized that any kind of permeable protective agent cannot form a protective layer on the outermost surface of the stone. Therefore, the stone that has been protected by the permeable protective agent should be treated with a surface protective treatment, that is, a surface protective agent is required. Stone can really be regarded as "double protection". Because any kind of excellent curing method of stone does not need waxing, the waxy layer is not breathable, but also easy to stick, and it is easy to make the color of the stone surface yellow. Use a surface type that is breathable and does not contain waxy substances. The agent can further protect the stone and the protective layer, and keep the natural bright color of the stone.

　　 Before choosing stone, its natural bright surface is also a factor that cannot be ignored. However, we must ensure that the physical properties of the stone are the greatest value of its use. Only by considering all the characteristics of the stone, the stone you choose can maximize their decorative practicality and aesthetics.