Kaolin, also called China clay, is nearly white in color. It is chemically inert, non-abrasive and possesses a number of characteristics that make it desirable for use in a range of industries, including paper and paperboard, paints and coatings, plastics, cosmetics, concrete and agriculture among many others. Kaolin is derived from the mineral Kaolinite which comes from the Earth’s crust. Kaolin was first discovered in China and the name comes from two Chinese characters that mean “high hill” (Kao-Ling).
Kaolinite is one of the most common minerals mined throughout the world. It is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world, kaolinite is colored pink, orange, or red by iron oxide, giving it a distinct color. Lighter concentrations yield white, yellow or light orange colors.
Kaolinite occurs in abundance in soils that have formed from the chemical weathering of rocks in hot, moist climates such as in tropical rainforest areas. If one were to compare soils along a gradient towards progressively cooler or drier climates, the proportion of kaolinite decreases, while the proportion of other clay minerals such as illite (in cooler climates) or smectite (in drier climates) increases. Such climatically-related differences in clay mineral content are often used to infer changes in climates in the geological past, where ancient soils have been buried and preserved.
In the US the primary kaolin deposits are found in central Georgia, on a stretch of the Atlantic Seaboard fall line between Augusta and Macon. The deposits were formed between the late Cretaceous and early Paleogene eras, about 100 million to 45 million years ago, in sediments derived from weathered igneous and metakaolin rocks. Kaolin production in the US during 2011 was 5.5 million tonnes. Highly technical equipment and processes are employed to transform the crude kaolin into high quality products which are marketed around the world for a wide variety of applications including cosmetics.
Kaolin is not nearly as absorbent as most clays that are used medicinally as it has a low shrink-swell capacity. Also, it has a low cation exchange capacity (CEC). This clay is sometimes referred to as 'white cosmetic clay'. Clay, in the form of kaolin, was once a common ingredient in western medicines such as Kaopectate, Rolaids and Maalox. Kaolin’s absorbent properties make it a popular ingredient in cosmetic clay masks and preparations for oily skin. Used too often in high amounts, it can be drying, but is otherwise a benign cosmetic ingredient.
Kaolin is registered as an Over-The-Counter (OTC) skin protectant drug with the FDA (Category I, allowed concentration 4-40%). This means that if you want to sell a finished product containing kaolin and you make any skin protectant claims (including minor cuts, scrapes, burns, chapped skin and lips, poison ivy, poison oak, poison sumac, and/or insect bites), kaolin must then be listed under 'Active Ingredients' on the label. This classifies your product as both a cosmetic and an OTC drug product. Also, your facility and your product must be registered with the FDA and you must operate under cGMP guidelines. However, if no skin protectant drug claims are made on the label, kaolin is not considered an OTC drug and no registration is needed.
It is recommended that United States Pharmacopeia (USP) Grade Kaolin be used in skincare applications. USP Grade means that a product meets all of the requirements as contained in the USP monograph for that product and has been manufactured in a cGMP compliant facility. (If there is no USP monograph, a material cannot be labeled as USP Grade.) Kaolin, USP has been screened for contaminants such as heavy metals and can safely be used as an extender and suspending agent in a variety of cosmetic preparations. It can be used in lotions, creams, powders, masks and color cosmetics as well as in bath bomb formulations.
The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for kaolin exposure in the workplace as 15 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 10 mg/m3 total exposure TWA 5 mg/m3 respiratory exposure over an 8-hour workday. It is recommended that protective gear such as respirator masks be used when handling kaolin to prevent excessive inhalation of this raw material.
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