Mineral Information and Data:

Al2Si2O5(OH)4 [CNMNC approved formula]

Named in 1867 for the ancient Chinese locality "Kaoling (Gaoling)", meaning high ridge.

IMA status : Approved Species 1980 ()
(8th edition) :  
  (71) Phyllosilicate Sheets of Six-Membered Rings
  (71.01) with 1:1 layers
  (71.01.01) Kaolinite group
(10th edition) :
  (09) Silicates
  (09.E) Phyllosilicates
  (09.ED) Phyllosilicates with kaolinite layers composed of tetrahedral and octahedral nets
Crystal system: Triclinic System
Point group (H-M): 1 — pedial
Unit cell: a = 5.16 Ǻ, b = 8.96 Ǻ, c = 7.41 Ǻ, α = 91.7°, β = 104.9°, γ = 89.8°
Crystal Habit: Thin hexagonal platelets or scales; elongated platelets or curved laths; massive compact, friable, mealy
Color: Colorless, white, yellowish pink, reddish, bluish
Diaphaneity: Transparent to translucent as single crystals
Luster: Pearly to dull earthy
Hardness (Mohs): 2 to 2.5
Measured Density: 2.6 to 2.63 g/cm3
Cleavage: 1; {001} perfect
Tenacity: Scales flexible, inelastic, plastic
Streak: White, or paler than the sample.
Polymorphism and Series: Polymorphous with dickite, halloysite, and nacrite
Geologic Setting: Replaces other aluminosilicate minerals during hydrothermal alteration and weathering. A common constituent of the clay-size fraction of sediments, where it may be formed by direct precipitation.
Mineral Association: Quartz, feldspar, muscovite
Synonyms/varieties: Anauxite (SiO2-rich var.), ancudite, carnat, collyrum, Fuller


Kaolinite pseudomorph after orthoclase (Carlsbad twinned)
Origin: St. Austell, Cornwall, England
Sample size: 5 x 2.5 x 1 cm
Photo: Rob Lavinsky


(zoom-in of above)


Beige massive kaolinite in quartz-feldspar veins
Origin: Roadcut along the old road (pre 1960) between St. Pietro and Castra, Corsica, France
Sample size: 5 x 7 cm
Photo: Diederik Visser


Kaolinite at this locality is commerically exploited by the Goonvean China clay Company; Kaolinite is used in the production of a number of products such as ceramics, paper, catalysts, toothpaste and paint.
Origin: Rostowrack Pit, St. Austell, Cornwall, U.K.
Sample size: 9 x 14 x 15 cm
Photo: Diederik Visser