Stone is from rock, and rock is consist of the mineral, the mineral contain iron is the source of the iron in stone, iron element spread widely in natural world, but most of them appear to be compound, iron element is belong to medium activity metal, under high temperature is easily to be strongly acted with oxygen,  sulfur, chlorine,  and easily dissolve in abio-weak acid solution and strong hydrochloric acid solution, at the same time, the strong alkali solution also corrade the iron.

     Therefore the iron could only exist in the state as compound (contain iron mineral). Iron compound are: oxid, sulfid, silicic acid iron, carbonic acid iron, boracic acid iron, etc… about several hundred kind. But mainly four kind as following:

oxid, include magnetic iron ore, red iron ore, brown iron ore, etc. sulfid, include yellow iron ore, white iron ore, yellow bronze ore, yellow tin ore etc. silicate mineral contain iron, include olive stone, black column stone, common picrite etc. carbonate mineral contain iron, include siderite, ankerite, etc.

     As the stone itself contain hematite and sulfur iron ore, this kind of ore could easily be oxide and cause rust and erosion, this cause the color change of stone surface, become yellowish and appear rusty spot etc.  more seriously is that after erosion, the rusty iron expand and cause crystal grain bursting and hole, below is the detailed description for the affection on the stone caused by iron mineral.

     Except the sulfate ore containing iron affect the granite, most of ore contain iron may exist in granite, silicic acid iron ore spread widest in area and quantity. Next are oxid and sulfid. Usually, the mineral contain iron, the color is darker, so it has key affection on the granite decoration value. If the darker mineral ore centralized, the stone usually show black, green, for example, MOCA green (contain FeO+Fe2O3：6.43%）、India black（contain FeO+Fe2O3：13.2%）、Africa black (contain FeO+Fe2O3：20.5%），Simphson black(contain FeO+Fe2O3：11.5%), etc. India black galaxy is the best example, the array of the iron ore make the stone beautiful look, and also could make the stone color change brilliant, like peacock green（contain FeO+Fe2O3：6.21%）、forest green（contain FeO+Fe2O3：5.31%）、leopard skin flower （contain FeO+Fe2O3：3.40%）etc.

     Sulfur-iron is the main reason for granite rusty stain, it could be hydrolyzed easily under normal temperature and normal pressure, and become the oxide, and further hydrolyzed to be limonite, after sulfur-iron is  decomposed, sometime it will leave the feint of cubic pyrite, some of which melted and cause many holes. If oxide solution seep and dye through the crack and pore, and become the iron film, stain the stone, cause the color difference, It will affect the stone decoration effect. The 2nd main reason to spoil the granite is biotite, flake state organization easily to airslaked and peel off the surface, after peeling off, it cause the pit on the surface, furthermore, biotite is quite often hydrolyzed and release Fe3, thus to affect other ore, which occur serious rusty spot. Lutetium iron (ie, chlorite ) is the third reason to spoil the stone. It become soil after airslake, under the effect of airblow and water, it cause the hole and pit on the stone surface.

     how the iron ore affect the marble
     the iron ore exist in marble are carbonic acid iron, sulfur iron, oxide and iron silicate mineral etc. their different content affect the marble quite different, the iron dolomite could make the marble become grey, and siderite make it brown, hornblende ore make the color to be green-inkgreen-black, appear to be spot state, line state, and appear to be a certain pattern, color change, in addition, the chlorite, will make the marble to be green or yellow green color. The rusty stain on marble, the main reason is pyrite, and then is magnetic pyrite, nickel pyrite, etc, its stain is the same reason as granite, after sulfur-iron is  decomposed, sometime it will leave the feint of cubic pyrite, some of which melted and cause many holes. (for example, new beige marble, the holes around 1-3mm are often seen) the chlorite this kind of ore, easily airslake, long time will cause pit or pore.

     The effect of iron content on the stone safety
     The percentage of the iron although do not decide the safety degree of stone, but from the cause of rusty stain of stone, it affect the stone greatly. It is the total summation of oxide iron content plus iron ore, usually to express it by FeOand Fe2O3 percentage (%), it could not show the content of the ore and and each content percentage, so it is also difficult to determine its anti-airslake. In granite and marble, if the ore is mainly to be more steady content, like ferrosilicon acid salt, instead of sulfur-iron, biotite, and iorn film, then the stone have strong ability to be anti-airslake .

     In one word, whatever marble or granite, the stability of iron ore decide the stone’s character of anit-airslake, among so many iron ore, the sulfur-iron is most not stable, and then biotite, and chlorite this kind or ore, therefore, when choose the stone, should pay attention to the this, so to ensure the safety of stone.

 

 

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