Why do stone walls change color?

When irradiated by white light, it will produce various optical phenomena such as absorption, transmission and reflection. If all the light is absorbed, this mineral is black; If all wavelengths of colored light in white light are uniformly absorbed, then minerals are gray; Basically not absorbed, it is colorless or white. If only some wavelengths of colored light are selectively absorbed, while others are transmitted or reflected, minerals will be colored. In addition, due to physical and optical effects such as light wave reflection, scattering and interference, color rendering will also be affected. Color depends on the inherent color of the mineral itself, which is called self-color. It is related to the chemical composition and internal structure of the mineral itself. The rock can selectively absorb pigment ions, crystal structure, electron transition, color center and other factors of a certain wavelength light wave, and the remaining complementary color light constitutes the true color of the mineral. The final color of rock reaction is the result of absorption of light waves with different wavelengths in white light. If it generally absorbs light waves of various wavelengths evenly, there will be black, gray, white and other colors with different absorption degrees. If it selectively absorbs light waves of various wavelengths, it will show various bright colors. If it contains impurities, it will show another color different from white, which is called heterochromatic. Generally, the color caused by impurities or bubbles is called heterochromatic, and wax stone is a typical heterochromatic. For example, wax stone is colorless when it is pure. When mixed with impurities, it can be dyed into yellow, red, purple, blue and other colors, but it turns purple or rose when it contains a small amount of (Fe3+), yellow when it contains a small amount of (Fe3+Cr3+), black when it contains a small amount of aluminum ions (Al3+), and black when it contains organic matter. When minerals are colored by other colors, the colors often change. Agate, for example, has various stripes due to the different formation time and coloring elements. These beautiful stripes make agate unique.