subject: Iron And Stone [print this page] Ordinary rocks become common stone products after fine processing. Stone is made of many kinds of mineral, such as iron minerals. In nature, iron element appear in the form of compounds, and its very easy produce chemical reaction with oxygen, sulfur, chlorine etc under high temperature conditions, and can be dissolved in inorganic dilute and concentrated hydrochloric acid .
Because the stone contains hematite or pyrite, and the kind of iron minerals can be oxidized easily and rust, cause many stone problems on the surface like discoloration and rust. And then we will illustrate each of influence respectively in the following paragraphs.
First, in addition to the iron sulfate minerals, most of iron minerals are likely to exist in granite in the form of various chemical formula. Whats more, the largest number of iron silicate minerals most widely distributed, and followed by the iron oxide. The deep color have a critical impact on the decoration, beautiful and value of granite. One hand, dark minerals are more concentrated , the stone often shows black and green color. In the other hand, pyrite ,white iron ore and other iron minerals are embedded in gabbros and contribute to flashing golden black stone. Due to the permutations and combinations of the iron minerals , the natural stones become colorful and brilliant.
Second, the iron sulfide is the major cause of yellow rust pollution. The iron sulfide would suffer from weathering and hydrolysis easily in the ambient temperature and pressure. First ,it will generate iron oxide, and then change into limonite. After decomposition, it would occur illusion of the cube of pyrite. Some of them dissolved into many holes. If the iron oxide solution penetrated into it and formed the iron film, the stone would be polluted and reduce the gloss of stone , finally, it effect the decoration. The second reason for destruction is biotite. Lamellar structure is easily stripping from the surface and weathering ,and form small pits.
Third, there are iron carbonate, iron sulfide, iron oxide and iron silicate minerals in the marble.
Due to the different components of iron-bearing minerals in the marble, the function is very different .Ankerite make marble grayed , amphibole minerals shows green, and chlorite makes marble green. The surface of marble suffer rust because of pyrite. The second is pyrrhotite which belongs to iron sulfide mineral. The mechanism of pollution is the same to granite.
In the chemical ingredients of stone, although the level of iron component can not judge the stone security level completely, its the main reason of rust for most of stone. The influence of the safety of stone can be quite large. Whether granite or marble stone, iron silicate minerals is more stable in the iron-bearing minerals instead of iron sulfide and iron film. Therefore, stone has strong wind resistance. On the contrary, if the iron-bearing minerals are mostly unstable iron sulfide, despite the low iron content, the ability of weather resistant would be poor.
All in all, regardless of marble or granite, the stability of the iron-containing minerals determine the stones resistance to weathering.
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