We often say that granite "will never fade." But in the long run, granite stone will fade, it's just time. In particular, building surfaces, squares, etc. are also affected when exposed to wind and sun. For example, red granite will fade after ten and a half months of exposure to the sun.
The minerals in granite are mainly composed of feldspar, quartz, mica, pyroxene, hornblende and so on. In the main silicate mineral structure, each silicon ion is surrounded by four oxygen ions to form a silicon-oxygen tetrahedron. This basic structural unit has very stable properties, strong acid and alkali resistance, hard to dissolve, weathering resistance, and good discoloration.
The fading of granite also varies with different types of stone. Generally speaking, darker lighter granite is easy to fade, because the mineral composition of darker (such as black, dark green) granite is mainly pyroxene, amphibole, basic plagioclase, and magnetite Wait. The light-colored granite is mainly acid plagioclase, potash feldspar, biotite, quartz and so on. Minerals are generally formed underground, some minerals are formed first, and some are formed later.
The first ones are often those with heavier atomic weight, deeper positions, less oxygen supply, and greater pressure; the latter ones are the opposite. Therefore, different minerals generally have different formation periods, and the order is roughly: dark minerals: olivine-pyroxene-hornblende-biotite; light-colored minerals: basic plagioclase-acid plagioclase-potassium long Stone-quartz. After the first minerals are exposed to the earth's surface, due to major changes in the environment, secondary changes are prone to occur, while the later formed minerals have less changes. The most stable one is quartz.
Another situation is that secondary minerals are easier to fade than primary minerals. For example, green and grass-green veneer plates with epidote chlorite as the main component have faded in color after 5-10 years, but they are similar to marble. In comparison, this change is still very weak. The color change (fading) is also related to the environment. The high acid-base content in the air in the industrial zone is easy to change and fade. In addition, the degree of maintenance is also very important.
Marble is mainly composed of minerals such as calcite and dolomite, and most of the former are common. The molecular formula of calcite is CaCO3, and dolomite is CaMg[CO3]2. Both have carbonate [CO3] ions. It is relatively active and easily interacts with sulfur dioxide in the air to form gypsum (Ca[SO4].2H2O), which is turbid. Particulate. Calcite easily interacts with water to form calcium bicarbonate (Ca[HCO3]2) that is dissolved in water and becomes calcium carbonate after the water is lost. After these changes, the original crystal polished surface of the marble polished plate no longer exists. Therefore, it is not suitable to use marble for exterior wall finishes, especially open-air finishes. As the exterior wall finishes, the color of marble will generally be discussed after 2 to 3 years.
