滑石(talc)是已知最软的矿物，其莫氏硬度标为1。用指甲可以在滑石上留下划痕。滑石一般为白色，略带青色或绿色。

滑石是其他矿物在地下发生长期的物理、化学变化而成的，属于一种“变质矿物”，通常由镁的岩石经变质而成。

比如由碳酸镁构成的白云岩，在富含硅的高温热液作用下，主要成分就可能渐变成水合硅酸镁，即滑石。

而一些含有橄榄石、顽火辉石、角闪石等其他含镁硅酸盐的岩石，也会在类似过程中发生成分重组，向滑石转变。

Talc is a clay mineral composed of hydrated magnesium silicate with the chemical formula H₂Mg₃(SiO₃)₄ or Mg₃Si₄O₁₀(OH)₂. In loose form, it is the widely used substance known as baby powder, also known as talcum powder. It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage, and the folia are non-elastic, although slightly flexible. It is the softest known mineral and listed as 1 on the Mohs hardness scale. As such, it can be easily scratched by a fingernail. It has a specific gravity of 2.5–2.8, a clear or dusty luster, and is translucent to opaque. Talc is not soluble in water, but is slightly soluble in dilute mineral acids. Its color ranges from white to grey or green and it has a distinctly greasy feel. Its streak is white.