The end-state for this transformation is referred to as "leather dry".
Between 100 °C and about 550 °C (1,022 °F), any remaining liquid water is expelled from kaolinite.
The end state for this transformation is referred to as "bone dry".
Subsequent transformations are not reversible, and represent permanent chemical changes.
Endothermic dehydration of kaolinite begins at 550–600 °C producing disordered metakaolin, but continuous hydroxyl loss is observed up to 900 °C (1,650 °F).
Although historically there was much disagreement concerning the nature of the metakaolin phase, extensive research has led to a general consensus that metakaolin is not a simple mixture of amorphous silica (Si O Finally, at 1400 °C the "needle" form of mullite appears, offering substantial increases in structural strength and heat resistance.
This is a structural but not chemical transformation. Kaolinite is one of the most common minerals; it is mined, as kaolin, in Pakistan, Vietnam, Brazil, Bulgaria, France, United Kingdom, Iran, Germany, India, Australia, Korea, the People's Republic of China, the Czech Republic, Spain and the United States.
Kaolinite has a low shrink–swell capacity and a low cation-exchange capacity (1–15 meq/100 g).
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 it is colored pink-orange-red by iron oxide, giving it a distinct rust hue.Lighter concentrations yield white, yellow, or light orange colors.Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, United States.Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.Kaolinite group clays undergo a series of phase transformations upon thermal treatment in air at atmospheric pressure.