The material is the product produced by the processing of the rock. The rock is composed of minerals, and the iron-containing mineral is the source of iron in the stone. Iron elements are widely distributed in nature, but most of them appear as compounds. Because iron is a moderately active metal, it reacts strongly with oxygen, sulfur, chlorine and other elements at high temperatures, and is easily soluble in inorganic dilute acids. In the solution of concentrated hydrochloric acid, the concentrated alkali solution also easily erodes iron. Therefore, iron can only be preserved in nature when it appears in the form of a compound (iron-containing mineral).
Iron compounds include oxides, sulfides, iron silicates, iron carbonates, iron borate, iron tungstate, iron sulfate, etc., but the following four compounds are the main categories:
1. Iron Oxide: Minerals containing iron oxides include magnetite, hematite, limonite, and ilmenite.
2. Iron sulfide: The minerals containing iron sulfide are pyrite, pyrite, brass sand, yellow tin ore.
Third, iron-containing silicate minerals: olivine, black garnet, cross stone, andalusite, ordinary pyroxene. 4. Iron carbonate minerals: there are siderite and iron dolomite.
Since the stone itself contains the above-mentioned iron-containing minerals such as hematite or pyrite, such iron minerals are easily oxidized and rusted, causing defects such as discoloration, yellowing and rust on the surface of the stone, and even severe corrosion due to iron. After expansion, crystal particles burst and holes. The effect of iron-containing minerals on each stone is explained item by item:
Effect of iron-containing minerals on granite stone
Except for iron-sulfate minerals, most of the iron-containing minerals may be present in granite, which is the most extensive and distributed of iron silicate minerals, followed by iron oxide or iron sulfide minerals. Generally, the color of iron-containing minerals is dark and dark, which has a critical impact on the decorative aesthetic value of granite. Among the dark minerals in granite, the stone is often black and green, such as Mocha green (including FeO+Fe2O3: 6.43%), Indian black (including FeO+Fe2O3: 13.2%), and South Africa deep black (including FeO+Fe2O3). : 20.5%), Zimbabwe black (including FeO+Fe2O3: 11.5%). Iron-bearing minerals such as pyrite and pyrite are embedded in gabbro, thus forming a black gold stone with glittering gold, and Indian black gold is the most prominent example. The arrangement and combination of iron-containing minerals in the stone enriches and beautifies the decorative aesthetic effect of the stone, making the natural stone color change beautiful, such as malachite green (including FeO+Fe2O3: 6.21%), forest green (including FeO+Fe2O3: 5.31) %), leopard skin flower (including FeO+Fe2O3: 3.40%).
Iron sulfide is one of the main reasons for granite to be contaminated by rust yellow. It is easily weathered and hydrolyzed under normal temperature and pressure to form iron oxide, which is further hydrated into limonite. After the decomposition of iron sulfide, sometimes the pyramidal pyrite illusion is left, and some dissolve into many holes. If the iron oxide solution infiltrates along the joint fissure surface, thereby forming an iron film, the stone is contaminated, forming a color difference, and reducing the stone decoration effect. The second main damage to granite is due to biotite. The flaky structure is easily peeled off along this surface and is easily weathered. After the weathered layer falls off, small pits are formed on the surface of the stone. In addition, biotite (K (Mg, Fe3 (Alsi3O10) (OH) 2) is often acted as an aqueous solution to release Fe3+, while rusting other minerals, producing severe rust. Iron-containing garnet, chlorite mineral is flower The third main cause of the destruction of granite is that they are easy to form soil after weathering, and after the wind blows water, holes and pits are formed on the surface of the stone.
Effect of iron-containing minerals on marble stone
The iron minerals in marble include iron carbonate, iron sulfide, iron oxide and iron-containing silicate minerals. The iron-containing minerals present in marble vary greatly in their effects on marble due to their different compositions. Iron dolomite can turn marble into gray, siderite becomes brown, and hornblende minerals appear green-ink-black. When they are dotted or linear, they form a certain pattern and produce their own richness. Color changes; in addition, chlorite, garnet will make the marble green or yellow-green.
Marble stone suffers from surface rust yellow due to pyrite, followed by ferroferric ore and nickel pyrite. The cause of pollution is the same as that of granite. After decomposition of iron sulfide, sometimes it will leave cubic yellow. Iron ore illusion, and some dissolve into many holes (such as 1~3mm aperture hole in new beige marble plate). The anti-weathering ability of garnet, chlorite minerals and iron-bearing minerals is poor, and pits and voids are formed over time.
Effect of iron-containing components on stone safety
Although the level of iron content in the chemical composition of stone does not completely determine the safety of stone, it is the main reason for the occurrence of lesions (rust spots) in stone itself, and has a considerable impact on the safety of stone. It is the sum of all iron-bearing minerals and the iron content of iron oxide attached to the surface of the stone. It is generally expressed as the percentage of FeO and Fe2O3. Therefore, it is difficult to determine the weathering resistance of the original mineral composition. Ability. As mentioned above, in granite or marble stone, if the iron mineral contained in the stone is mainly composed of iron silicate minerals rather than iron sulfide, biotite and iron film, the stone has Strong anti-weathering; on the other hand, if the iron-containing minerals in the stone are mostly unstable iron sulfide, biotite, etc., although the iron content is low, the stone's ability to resist weathering may become poor.
All in all, whether it is marble or granite stone, the stability of iron-containing minerals determines the weathering resistance of stone. Among many iron-bearing minerals, iron sulfide is the most unstable component, followed by biotite, and Iron-bearing garnet and chlorite minerals. Therefore, when selecting stone or identifying stone lesions, attention should be paid to the distribution and content of these harmful minerals and the weathering resistance of iron-containing minerals to ensure the safety of the stone.
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