The mineralogy name of vermiculite is from Latin, with the meaning of "wormlike" and "worm trail". Vermiculite is a kind of hydrous iron magnesium aluminum silicate mineral, and it is bending like the leech, so it is called "Zhishi" in Chinese. It is formed by biotite (flogopite) by supergene weathering or hydrothermal alteration. Its chemical composition is (Mg,Fe,AL) 3[(Si,AL)4O10(OH)2]·4H2O, but often changes. Vermiculite is monoclinic system, and plate shaped. 

Color: brown, cinnamon or bronze. Oily luster. Hardness:1~1.5, density : 2.4~2.7g/cm3. There are two kinds of shape: coarse and fine. The coarse ones are transformed by biotite (flogopite) and keep the characteristics of mica flake and scale; the fine ones like earth, and it is difficult to distinguish for mixed with other clay minerals. After roasted on the temperature of 800-1000℃ for 0.5-1 minute, the volume of vermiculite expands rapidly by 8-15 times, some up to 30 times. The average unit weight of expanded vermiculite is 100~130Kg/m3. The expanded vermiculite has tiny air buffer, so it has good thermal insulation property.