Characteristics of Montmorillonite Clay

Color and Appearance

• Montmorillonite has the appearance of a dull, massive mineral, which is typically white, but the clays may be pink, grey or tinted with yellow or green, depending on the concentration of the minerals that make up the clay. For instance, the pink and red clays contain a high concentration of manganese. The ratio of the minerals that make up the clay varies according to the source.

Hardness

• Montmorillonite clay is one of the softest clays due to the high concentration of small mineral particles. The clay has a hardness of 1 to 2 on Mohs hardness scale. On this scale, the hardest mineral is diamond, at 1,600. The specimens of montmorillonite clay may vary in hardness, depending on their source, but typically the clays are soft and malleable. Clays that contain a high percentage of impurities are harder.

Luster and Diaphaneity

• Luster is the way light interacts with the material. Montmorillonite clay is earthy, which is a term used to describe materials with the appearance of dry mud. This clay has low luster, due to the fine grained minerals in its composition. The clay's diaphaneity, or the transparency quality, is translucent to opaque, depending on the type of crystals that make up the material. The material is not fluorescent. However, if it contains autunite, it may glow in the dark.

Expands When Added to Water

• Montmorillonite clay expands when added to water. The degree to which it swells depends on the composition of the clay and the molecular spaces between the layers. For this reason, the clay is used as a water-clogging material. Montmorillonite clay is also used in the oil drilling industry as a drilling mud, keeping the drill cool. The material is sometimes used as a cosmetic treatment, applied externally in the form of masks. According to Eytons' Earth website, the clay may also be used internally as a cleanser or to promote healthy digestion.