Talc is a hydrothermal alteration mineral. Magnesium-rich minerals are often changed to talc by hydrothermal alteration.

Talc is a mineral with a layered structure. Pseudo-hexagonal lamellar single crystals are rare, generally dense blocky, bladed, fibrous or radial aggregates. A group of extremely complete disintegration, flakes with flexure. Slippery, in water does not fall apart. Odorless, tasteless, adiabatic and insulating.

Medicinal identification

The talc herb is flat, rhomboid or irregular block, size varies. All white, egg green or yellowish white, the surface has a pearl-like luster, translucent or opaque. The texture is soft and delicate, the hand has a slippery feeling, with the finger can be scraped off the white powder.

Odorless, tasteless, with a slightly cool feeling. To neat, color green and white, smooth, no miscellaneous stone is good. Microscopic identification: under the transmission polarizing microscope: colorless and transparent in thin section. Low positive protrusion. The highest interference color up to three orange, some talc highest interference color only reaches the middle of the second level. Nearly parallel extinction (slip angle only 2°-3°). Positive prolongation sign. Biaxial crystal. Negative optical properties. Refractive index Np=1,538-1.550,Nm=1.575-1.594; birefringence Ng-Np=0.030-0.050.

Baidu Encyclopedia - Talc