The chemical formula of mineral Montmorillonite is indicated by (Na,Ca)(Al,Mg)6(Si4O10)3(OH)6-nH2O or Hydrated Sodium Calcium Aluminum Magnesium Silicate Hydroxide. Montmorillonite is actually a Silicate mineral. Montmorillonite is most commonly used as drilling mud and as a water clogging agent in soil. Mineral Montmorillonite is also a member of the general mineral group called clays. Montmorillonite typically forms microscopic or at least very small platy micaceous crystals. According to several observations made in the field of optical mineralogy, the water content is said variable, and in fact when water is absorbed by the crystals they tend to swell to several times their original volume. This makes montmorillonite a useful mineral for several purposes. Montmorillonite is the main constituent in a volcanic ash called bentonite, which is used in drilling muds. The bentonite gives the water greater viscosity(”thickness” of flow), which is very important in keeping a drill head cool during drilling and facilitating removal of rock and dirt from within a drill hole. Another important use of montmorillonite is as an additive to soils and rocks. The effect of the montmorillonite is to slow the progress of water through the soil or rocks. This is important to farmers with extended dry periods, engineers of earthen dams or levees or perhaps to plug up old drill holes to prevent leakage of toxic fluids from bottom levels to higher aquifers used for drinking water.

            It is important to note that Montmorillonite does not get much consideration as a mineral specimen. Usually, the pure samples of Montmorillonite are usually found massive, dull and not very attractive. However, there are also exceptional Montmorillonite specimens that defy the norm. Mineral Montmorillonite has been found as attractive pink inclusions in quartz crystals and these actually make for interesting specimens. Montmorillonite is most commonly found white, gray, or pink in color with tints of yellow or green that could appear more fascinatingly wonderful when viewed with the aid of petrographic polarizing light microscope. Montmorillonite is usually found dull in appearance.

            Most Montmorillonite crystals are found translucent in appearance while masses are commonly found opaque. Montmorillonite is known to crystallize in the monoclinic system of crystal formation. In the field of optical mineralogy, the monoclinic system of crystal formation comprises crystals having three axes of unequal lengths. Two of which are usually found in a position that is oblique or not perpendicular to one another. However, both of which are commonly found perpendicular to the third axis. The crystal habit of mineral Montmorillonite as described in the field of optical mineralogy is never in large individual crystals but usually in compact or lamellar masses. Montmorillonite is also seen as inclusions in quartz as fibers and powder-like masses. Mineral Montmorillonite is most commonly found showing perfect cleavage in one direction that is usually basal when viewed with the aid of polarizing microscope for mineralogists. It is however important to note that this cleavage cannot be seen in massive Montmorillonite specimens.

            Montmorillonite is most commonly found showing uneven to lamellar fracture when specimen is evaluated using the petrographic polarizing light microscope used in the field of optical mineralogy. The hardness measure of mineral Montmorillonite when it is evaluated using the Mohs scale method is usually found ranging from 1 to 2, which can sometimes leave marks on paper. The specific gravity measure of mineral Montmorillonite is usually found variable from 2.3 grams per cubic centimeters to 3 grams per cubic centimeters, which is considered average. When Montmorillonite specimen is rubbed on a white porcelain streak plate, it is commonly found leaving a white streak. Montmorillonite crystals may expand to many times their original volume when added to water. Montmorillonite is most commonly found associated with other interesting minerals including clays, biotite, and garnets. Montmorillonite notably occurs in France, Italy, USA and many other localities in the world. The best field indicators of mineral Montmorillonite usually include color, softness, luster, soapy feel, and expandability when added to water.