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

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)