Kaolinite

Mineral Name: Kaolinite (A.K.A: China clay or Kaolin)

Chemical Composition: Al2Si2O5(OH)4(2)

Color: Can be found ranging from white to yellow, and occasionally beige.

Streak: White (2)

Hardness: 2-2.5 (2)

Cleavage/Fracture: Kaolinite has 1 plane of cleavage, though it's very hard to see do to the small size of individual crystals.

Crystal Form: Kaolinite is microcrystalline with tiny grains and plates that can rarely be visible to the naked eye. (2)

Luster: Earthy or Dull (2)

Special Features: Has a plaster, or chalk-like texture. The outer layer will crumble easily into a smooth powder.

Varieties: The most often seen is Pianlinite, which is a variety specifically from Pianling, Xiuyan Co., China. (2)

Mineral Group: Kaolinite belongs to the silicate and phyllosilicate groups. Silicates are a group of minerals that contain different amounts of silicon and oxygen atoms. (2) Phyllosilicates join together with an atomic structure of each silicate tetrahedron surrounded by 4 oxygen atoms, 3 of which are shared with another tetrahedrons oxygen atoms (9). This configuration leads to the formation of distinct sheets. These sheets are bonded with layers of other elements and this gives phyllosilicates a distinct cleavage.(9)

Environment: Kaolinite can be found in clay deposits. (2) It is created as a by-product of alumino-silicate mineral aging. (3) When the bonds in the alumino-silicates are subject to weathering, and they break down and form kaolinite.

Associated Rock types: It is most commonly found in clastic sedimentary rocks, like shale. Clastic rocks are made up of bits of other rocks that have been broken down and made into other rocks (8). You can also find minerals weathering into kaolinite as granites chemically decompose and in impure chemical precipitate sedimentary rocks, like limestone.

Occurrence in North America: Kaolinite can be found in the following states in Northern America; Georgia, South Carolina, North Carolina, Arkansas, New Mexico, and also Quebec Canada. (5)

Economic: Kaolinite is the main, raw material used in the production of traditional pottery and ceramics. The powder is mixed with clay and other materials in order to make it more malleable. (4) Surprisingly, kaolinite is also used in the production of magazines and paper. When kaolinite is refined, it is used to coat the pages to give them the a special gloss that separates magazine paper from simple newsprint. (6)

It’s used in ceramics as a clay, used in paint, and plastic, but one surprising use is in toothpaste. After much refining, and grinding down, the kaolin particles are used as a sort of polishing sand to smooth your teeth and ship away plaque.(7)

Industrial Uses: Kaolinite has many different industrial uses, some of which include; rubber, ceramics, paint and plastics. It is also used in the production of paper products. Kaolinite is used as a filler, it makes the paper whiter and smoother to print sharper images on. (10)

First Notable Identification: Kaolinite is named after the Kao-Ling Mountain of the Jiangxi province of China, where it was discovered in high volumes. (2) It was also found in Europe around the 1700’s. It was thought to have been sent to Europe from China by a French Jesuit missionary as an example of materials used in porcelain (9).

How We Identified It: Kaolinite is 2-2.5 on Moh’s hardness scale and can be chipped with your fingernail. Kaolinite also has a chalky, plaster texture. It is smooth to the touch and leaves a white residue on your fingers. It almost resembles sheet rock, but with a much softer texture.