Refers to the pulp containing clay minerals, iron oxide and other mineral impurities, also known as liver stone. Its impurity content often reaches more than 15%. Because the texture is impure, it is usually opaque or slightly transparent, and its luster is slightly darker than that of ordinary chalcedony. Bish also has rich colors. Its varieties are divided by color, including red, green, white and yellow. In fact, tourmaline is often uneven in texture and varied in color. In addition to monochrome varieties, variegated varieties are also common. A tourmaline with red and brownish red spots on a dark green background is called "blood drop stone" or "blood star stone", "blood star stone" and "blood stone", which is very beautiful because of its large color contrast and strong visual effect. In the jewelry customs of many countries, it, together with aquamarine, is designated as the birthstone of March, symbolizing calmness, courage and wisdom. When there are more than two colors in tourmaline to form various strip or landscape patterns, they are collectively called "painted tourmalines", and can also be specifically divided into strip tourmalines and landscape tourmalines. And most of them are directly used as ornamental stones.