Kaolinite, a white clay mineral, is among the first pigments. It's created by the weathering of minerals found in stone. Present in igneous, metamorphic and sedimentary rock beds, kaolinite is a plentiful earth pigment used since the pre-Neolithic as a natural coloring.
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Kaolinite is naturally whitish in tone but may be colored pale pink, cream, brown, gold, yellow and sometimes blue or green. Tan and brown are the most common color variations. For a brighter white the pigment needs more processing.
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Tints come from inclusive earth pigments such as yellow and red ocher, or trace metals such as copper, or more rarely, iron. Muscovite (mica), quartz, feldspar, a mineral making up 60% of the Earth's crust; and anatase (a black oxide mineral) are also found in kaolinite.
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A relatively soft rock, kaolinite measures 2 - 2.5 on the Mohs scale of hardness, about the same as gold. Copper is 3 and glass is 5 - 6 for comparison. Kaolinite can be scratched with a fingernail or knife.
Kaolinite has a dull to earthy luster and leaves a white streak. Formations of kaolinite north Europe happen in the Mesozoic Era, 252-66 million years ago. Kaolinite and its parent stone kaolin exist in the upper part of the Earth's crust, from surface to c. 1.5 km (0.9 mi) down.
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Kaolinite clay is prevalent in soils formed by chemical weathering of rocks in hot, moist climates such as tropical rainforests. As soils progress to cooler or drier regions, the proportion of kaolinite decreases.
Proportion of other clay minerals such as illite (in cooler climates) or smectite (in drier climates) increases. Smectite is often found in volcanic zones. The main source of smectite is weathering of volcanic ash after contact with seawater.
Rocks abundant in kaolinite and halloysite, a chalky white mineral, are known as kaolin or China clay. They're both phyllosilicates, a group of minerals including the micas, chlorite, serpentine, talc and clay minerals, also called the Kaolinite-serpentine group.
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Among the most common minerals of the earth's crust, kaolinite is mined as kaolin in Brazil, Australia, Bulgaria, China, Czechia, France, Germany, India, Iran, Malaysia, South Africa, South Korea, Spain, Tanzania, Thailand, United Kingdom, United States and Vietnam.
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Kaolin clay is also called China clay due to its popular source in that country. Processed kaolin is a coating for paper, still used today throughout the world. The world kaolin comes from Gaoling (Kao-ling), a Chinese village near Jingdezhen in southeast China.
It's also simply called white clay. Kaolin clay is valued for porcelain and ceramics (china), paint, natural health, cosmetics and industrial properties. Among the earliest colors of the human palette, it's found in prehistoric cave paintings and tribal body decor.
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Kaolin clay is reduced to a powder product by soaking, washing and straining to remove impurities. The terms kaolin and kaolinite are often used interchangeably. Kaolinite is a pure clay mineral crystal, found in kaolin. Kaolinite is one part alumina and two parts silica.
Kaolin is a parent rock found in sedimentary deposits mixed with kaolinite, quartz particles, feldspar, silica, zinc, copper and magnesium. Most other clay minerals derive from kaolin.
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Minerals are separated from clay using wet processing methods. Wet separation uses water or other liquids, such as organic solvents, to separate minerals based on properties such as specific gravity or surface tension.
Hydrophobicity (in which a mineral is repelled by water) is a typical processing treatment. Kaolin clay is water-loving while some of its constituents, like talc, are water-repulsive.
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The desire to eat clay, diagnosed as the compulsive eating disorder pica, may be caused by the body's need for zinc (or iron in red clays). Symptoms of zinc deficiency include:
loss of hair
changes to skin and hair
infections
wounds slow to heal
eye problems
loss of taste and smell
diarrhea
Kaolin clay is given as a folk remedy for diarrhea. It also provides natural exfoliation by absorbing dead skin cells and impurities. It may treat or prevent skin problems like acne. Kaolinite is used as a whitener in toothpaste. It has a low iron content and is odorless.
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Clay absorbs moisture and oils, thus isn't recommended as a hydrating treatment. It's effective for cleansing oily skin. For potters and ceramics workers, human skin oil gives the clay more elasticity, which is why clay is worked with the hands.
White is among the three color hues an infant can perceive after being born, along with black and red. These are also favorite palettes of early humans as they're easily found in natural form.
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Black is often acquired from ground magnetite, one of the three major iron oxide ores. From magnetite, it's the natural version of synthetic color Mars Black. Black from lamp soot is sold standardized as Lamp Black. Black also comes from charcoal or charred bone.
Grinding colors is one of the labors common in scribe schools, dye and pigment making, and artwork. Through history, apprentice or student scholars are tasked with grinding and preparing raw pigments. Pigment processing goes back c. 300,000 years ago to Africa.
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Red in the ancient world comes from ground hematite (red ocher) or raw red ocher; also the kermes insect, Polish cochineal bug or madder root.
In the 1500s The Portuguese bring a brilliant red from the New World cochineal bug. It's often a bright red pigment in Mesoamerican art. Cochineal bugs produce the color carmine.
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In mining the mineral rock is cut from the quarry. In the stone age people use flint to quarry rocks like limestone and kaolinite. For today's demand, strip mining is the most effective method, involving specifically top layers of the earth's crust where kaolin is often found.
Industrial safety:
Kaolin is generally recognized as safe, but may cause mild irritation of the skin or mucous membranes. Kaolin products may also contain traces of crystalline silica, a known carcinogen if inhaled.
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