Kaolinite is a distinct clay mineral. The term mineral kaolinite defines the name for a closely related clay mineral group, kaolin. It is also the name for the most abundant individual member of the same group. As one of the most common clay minerals, the use of kaolinite for various industrial and commercial applications are widely available.
Historical Background at a Glance
Kaolinite was presumably one of the most significant minerals in the prehistoric era. It was particularly true with the use of clay for pottery during this age. The Sumerians even granted a distinct symbol for this clay mineral.
Furthermore, in the thirteenth century, the Mongol dynasty (Yuan) dubbed kaolinite as the “Kaolin earth“. In 1637, Song Yingxing, a great scientist during the late Ming dynasty, thoroughly described it in his encyclopedia book entitled “Tiangong Kai Wu“. In 1712, a French priest introduced kaolinite to the western world in his report about the Jingdezhen porcelain.
Chemical Characteristics of Mineral Kaolinite
In mineralogy, the kaolinite chemical formula is Al2Si2O5(OH)4. It is an aluminum silicate in composition. The basic structural unit hence is the combination between an aluminum sheet and a silica sheet.
In detail, it is a 1:1 dioctahedral aluminosilicate layer. The silicate sheets (Si2O5) have a tight bonding with the aluminum hydroxide layers (Al2(OH)4).
Kaolinite has a non-swelling characteristic. It derives from the close bonding of hydrogen that typically prevents water molecules from penetrating between layers. Kaolinite is also relatively low in its capacity of ion exchange. It is due to the absence of a net electrical charge in each kaolinite layer. As a result, there isn’t a large cation of potassium, sodium, or calcium between kaolinite layers.
In addition to kaolinite, all the members in the kaolin group commonly have a similar chemical formula. They are, among others, dickite, nacrite, halloysite, and odinite. Kaolinite is a member of the kaolinite subgroup (dioctahedral) and the serpentine subgroup (trioctahedral), hence the kaolinite-serpentine group.
On the other hand, in common ceramic uses, kaolinite has different formula due to the oxide term, namely Al2O3·2SiO2·2H2O.
Physical Characteristics of Mineral Kaolinite
On its own, kaolinite can be dreary or uninteresting in characteristics. However, this mineral sometimes creates such more interesting pseudomorph formations. Also, kaolinite is a prevalent add-on to other minerals such as gem crystals, especially in the decaying feldspar pegmatites.
Mineral kaolinite is a clay mineral that mostly found in masses of what-so-called clay beds. It has such an earthy clay-like texture and odor with a soft consistency. As a friable mineral, kaolinite is an earthy, uneven fracture that easily breaks or crumbles. Therefore, you can cut and mold or shape it, especially when moistened or wet.
You can find them in typical bright white color to cream and pale yellow. The minerals also show usual browns to light browns, tans, and different hues due to the frequent mixture or staining. For example, some kaolinites exhibit a unique rust hue mainly by the impurities of iron oxide. The tints are red color to pink to orange or light orange. Occasionally, also the blue shades from other minerals.
Some terms to describe the lustre of kaolinite are often earthy, waxy, dull, or pearly. Lustre here means the light character the minerals reflect. This mineral is also opaque or translucent in its transparency category.
Industrial and Commercial Uses of Mineral Kaolinite
Thanks to its low shrink-swell and low cation-exchange capacities, kaolinite has a significant role in various industrial and commercial applications. The following are the most common use of kaolinite clay minerals:
- Paper production. The production of paper has been the biggest user of kaolinite in percentage. The industry uses this mineral to ensure the gloss for coated papers of specific grades.
- Pottery and ceramics. Since pre-historic times, kaolinites have been the main component in porcelain making.
- Pharmaceuticals. Kaolinite is an active ingredient in medications like soothing the stomach, diarrhea, digestive problems, nausea, and more. This mineral also has the capability of inducing and accelerating blood clotting in diagnostic procedures.
- Paint. This clay mineral can extend the white pigment of titanium dioxide (TiO2) and modify paint gloss levels.
- Rubber. Kaolinites modify the rubber properties during the vulcanization process.
- Light bulb. The application is as a light-diffusing element, especially in light bulbs with white incandescent.
- Soaps and facial masks.
- Organic farming. Kaolinite application as a spray to control the crop pest or prevent crop damage by the insect.
- Whitewash. The traditional Nepal masonry uses this white clay to paint the upper part of their stone houses.
- Spa body treatments. They use kaolinites in body wraps, cocoons, and feet, hands, and back spot treatments. Additional essential oil usually can give a more pleasant odor for this purpose.
- Absorbents. The application is for water or wastewater treatment systems.
The Geophagia – White Dirt Eating Habit
Apart from the above uses, there is also what-so-called geophagia or geophagy. It is a practice of directly eating kaolin – the white dirt – for health or hunger-suppressing purposes. Geophagia is an old practice that even recorded in the earliest of humankind history.
Many societies around the globe show this habit, especially the greater consumption among women during their pregnancy. In the southern part of the United States, for example, people call this clay mineral not only white dirt but also chalk or simply white clay.
The kaolin mines in the world are, among others: in Asia (Indonesia, Malaysia, Pakistan, Vietnam, the People’s Republic of China, South Korea, India, Iran, and Bangladesh); in Europe (the United Kingdom, Bulgaria, Spain, Germany, French, and the Czech Republic); in Africa (South Africa and Tanzania); and in America (the United States).
The most common kaolinites in western and northern parts of Europe are kaolinitic saprolite mantles. They belong to the Mesozoic-to-Early Cenozoic mantles in age. In the United States, Sandersville is famous as the “Kaolin Capital of the World“. Meanwhile, the thirteen counties in central Georgia have a nickname of the “white gold” due to their abundance of kaolin deposits.
Kaolinite, hence kaolin, derives its name from “Kao-Ling” (or “Gaoling“, which means “high ridge“). It is a Chinese mountain and a village located near Jingdezhen in the southeastern Jiangxi province in China.
Since the early times, the mineral kaolinite has been one of the most common and the most abundant clay minerals on Earth. Commercially and world widely mined as natural resources, this distinctive mineral indeed offers many beneficial uses.