Take pearlescent pigments as an example, pearlescent pigments are a class of pigments with pearl luster, which are deposited on the substrate (generally natural mica, synthetic mica, glass sheet and other sheet-like materials) above a layer or alternately deposited multiple layers of metal oxides or non-metallic oxides and formed a flat sandwich body with a structure similar to sandwich. Due to the difference in refractive index between the substrate and the oxide deposited on its surface and each oxide, when the light shines on the surface of the pearlescent pigment, the incident light will be refracted and reflected at the interface of each layer of the pearlescent pigment, and the color of the pearlescent pigment that people see is the result of the superposition of light after multiple refractions and reflections of the light, that is, the interference phenomenon of light.

Mica has a wide range of uses, in ancient China, it is often used to do traditional Chinese medicine, the ancients even think that taking mica: a year to remove all diseases (heavy metal poisoning), three years of long service, husband into a boy (body scrap), Zhongshan uncle Qing suit, over time can become a cloud (soul ascension). However, in the era without glass, the transparency of mica makes it a better decorative material, for example, we are familiar with the mica screen candle shadow deep, the river gradually falling Xiaoxing sink. Mica screen is low, tassel tent is small and mica calf car.

Natural mica powder and synthetic mica powder also have great differences in electrical insulation, mechanical properties, chemical stability, application range and cost. Natural mica powder has good electrical insulation, but the volume resistivity is lower than that of synthetic mica. Synthetic mica powder has better electrical insulation properties, high volume resistivity and stable dielectric constant, and is suitable for high performance electrical insulation materials. The hardness of natural mica powder is relatively low (2-3), and it has good elasticity and peeling property. The hardness of synthetic mica powder is higher (between 3 and 4), and the tensile strength and compressive strength are better than that of natural mica powder. Natural mica powder is stable in acid-base solution, but it is easy to decompose at high temperature. Synthetic mica powder is stable to acid and base at room temperature, but will be slowly corroded by sulfuric acid above 300℃. Better thermal stability, not easy to release gas. Natural mica powder is widely used in electrical appliances, welding rods, rubber, plastics, paper making, paint and other fields. Synthetic mica powder is mainly used in high-end electrical insulation materials, aviation, aerospace, national defense industry and other high-tech fields. Because synthetic mica powder needs to be produced through complex chemical processes, its production cost is usually higher than that of natural mica powder. Therefore, in the market, the price of synthetic mica powder is often higher than that of natural mica powder. However, with the continuous progress of production technology and the gradual emergence of scale effects, the price of synthetic mica powder is expected to gradually decrease.

The common characteristics of mica group minerals are: layered silicate minerals, monoclinic crystal system, a few trigonal crystal system, the crystals are pseudo-hexagonal columnar, plate and sheet; The aggregate is scaly and foliaceous. It has a set of extremely complete cleavage, along which it is easy to peel into sheets. Therefore, the shape of mica is usually regarded as sheet.

A group of parallel cleavages can be seen in a photograph of biomica under orthogonal polarized (left) and single polarized (right) mirrors.