Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$Mg$	Magnesium	element	3 - 5.06		constituent element	main
	$Fe^{2+}$	Iron(II) cation	element	0 - 2		constituent element	main
	$Al$	Aluminium	element	1 - 2		constituent element	main
	$Si$	Silicon	element	3 - 3.25		constituent element	main
	$O$	Oxygen	element	18		constituent element	main
	$H$	Hydrogen	element	8		constituent element	main

Composition comments

Common impurities: Ca (replace Mg, $Fe^{2+}$) and Cr, $Fe^{3+}$ (replace Al)

Chemical functions

	Function	Number
	$(OH)^-$	8

Chemical bonds

	Bond	Number
	$O^--H$	1

Oxides

Formula	$MgO$	$Al_{2}O_{3}$	$FeO$	$SiO_{2}$	$H_{2}O$
Mass fraction (%)	25.39	17.13	15.09	30.28	12.11

Oxides comments

for $(Mg_{3.75},Fe^{2+}_{1.25})Si_3Al_2O_10(OH)_8$

Strunz

Class

silicates (09)

Division

phyllosilicate (09.E)

Family

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

Code

09.EC.55

Dana

Major class

silicates (VIII)

Class

phyllosilicate sheets of six-membered rings (71)

Type

interlayered 1:1, 2:1, and octahedra (71.04)

Group

Chlorite group (Tri-Dioctahedral) (71.04.01)

Code

71.04.01.04

Phase type

crystalline

Crystal system

monoclinic

Crystal class

prismatic

Crystal class symbol

2/m (C2h)

Crystal spacegroup

C2/m

Refringence type

biaxial

Refringence sign

positive

Birefringence

0.005 - 0.011

Refraction index $n_{\alpha}$

1.571 - 1.588

Refraction index $n_{\beta}$

1.571 - 1.589

Refraction index $n_{\gamma}$

1.576 - 1.599

Dispersion V

r < v

Pure color

white

Color

white, blackish green, bluish green, yellowish green, olive green, pink

Diaphaneity

transparent to translucent

Luster

pearly

Links

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