IMA Code

Gmd

	Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$Cr$	Chromium	element	1		constituent element	main
	$O$	Oxygen	element	2		constituent element	main
	$H$	Hydrogen	element	1		constituent element	main

Chemical bonds

	Bond	Number
	$>Cr-O$	2
	$-O-H$	1
	$-O \dots H-$	1

Oxides

Formula	$Cr_{2}O_{3}$	$H_{2}O$
Mass fraction (%)	89.4	10.6

Strunz

Class

oxides - hydroxides - arsenites (04)

Division

hydroxides (without V or U) (04.F)

Family

Hydroxides with OH, without H2O; sheets of edge-sharing octahedral (04.FE)

Code

04.FE.20

Dana

Major class

oxides and hydroxides (III)

Class

hydroxides and oxides containing hydroxyl (06)

Type

where X+++O OH (06.01)

Group

-Grimaldiite- group (06.01.05)

Code

06.01.05.01

Phase type

crystalline

Crystal system

trigonal

Crystal class

ditrigonal-scalenohedral

Crystal class symbol

-3m (D3d)

Crystal spacegroup

R-3m

Refringence type

uniaxial

Refringence sign

negative

Birefringence

0.18

Refraction index $n_o$ (w)

2.155

Refraction index $n_e$ (e)

1.975

Pure color

red

Color

dark red, reddish brown

Diaphaneity

opaque

Luster

metallic

Links

• MinDAT: Grimaldiite
• WebMineral: Grimaldiite