Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$Na$	Sodium	element	0.3		constituent element	main
	$Fe^{3+}$	Iron(III) cation	element	2		constituent element	main
	$Si$	Silicon	element	3.65 - 4		constituent element	main
	$Al$	Aluminium	element	0 - 0.35		constituent element	main
	$O$	Oxygen	element	12		constituent element	main
	$H$	Hydrogen	element	2		constituent element	main

Composition comments

Typical formula: $Na_{0.3}Fe^{3+}_2.(Si_3Al)O_{10}(OH)_2 \bullet 4(H_2O)$ - Common impurities: Ti, Mg, Ca

Chemical functions

	Function	Number
	$(OH)^-$	2

Chemical bonds

	Bond	Number
	$O^--H$	1

Oxides

Formula	$Na_{2}O$	$Fe_{2}O_{3}$	$Al_{2}O_{3}$	$SiO_{2}$	$H_{2}O$
Mass fraction (%)

Strunz

Class

silicates (09)

Division

phyllosilicate (09.E)

Family

with mica sheets, composed of tetrahedral and octahedral nets (09.EC)

Code

09.EC.40

Dana

Major class

silicates (VIII)

Class

phyllosilicate sheets of six-membered rings (71)

Type

with 2:1 clays (71.03)

Group

Smectite group (Dioctahedral Smectites) (71.03.01a)

Code

71.03.01a.03

Phase type

crystalline

Crystal system

monoclinic

Crystal class

prismatic

Crystal class symbol

2/m (C2h)

Crystal spacegroup

C2/m

Refringence type

biaxial

Refringence sign

negative

Birefringence

0.030 - 0.035

Refraction index $n_{\alpha}$

1.53 - 1.58

Refraction index $n_{\beta}$

1.555 - 1.612

Refraction index $n_{\gamma}$

1.56 - 1.615

Dispersion V

strong

Pure color

green

Color

greenish yellow, brownish green, olive green

Diaphaneity

translucent to opaque

Luster

earthy

Links

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