Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$Al$	Aluminium	element	2		constituent element	main
	$Si$	Silicon	element	2		constituent element	main
	$O$	Oxygen	element	9		constituent element	main
	$H$	Hydrogen	element	4		constituent element	main

Composition comments

Common impurities: Fe, Mg, Na, K, Ti, Ca, $H_2O$

Chemical functions

	Function	Number
	$(OH)^-$	4

Chemical bonds

	Bond	Number
	$O^--H$	1

Oxides

Formula	$Al_{2}O_{3}$	$SiO_{2}$	$H_{2}O$
Mass fraction (%)	39.5	46.55	13.96

Strunz

Class

silicates (09)

Division

phyllosilicate (09.E)

Family

with kaolinite layers composed of tetrahedral and octahedral nets (09.ED)

Code

09.ED.05

Dana

Major class

silicates (VIII)

Class

phyllosilicate sheets of six-membered rings (71)

Type

with 1:1 layers (71.01)

Group

Kaolinite group (71.01.01)

Code

71.01.01.02

Phase type

crystalline

Crystal system

triclinic

Crystal class

pedial

Crystal class symbol

1 (C1)

Crystal spacegroup

P1

Refringence type

biaxial

Refringence sign

negative

Birefringence

0.007

Refraction index $n_{\alpha}$

1.553 - 1.563

Refraction index $n_{\beta}$

1.559 - 1.569

Refraction index $n_{\gamma}$

1.560 - 1.570

Dispersion V

r > v weak

Pure color

white

Color

white, brownish white, grayish white, yellowish white, grayish green

Diaphaneity

transparent to translucent

Luster

earthy

Links

• Wikipedia
• Webmineral database
• Mindat
• Handbook of Mineralogy (Min. Soc. Am)