Vivianite
Fe3(PO4)2*8H2O

Crystal symmetry

Monoclinic 2/m

Unit cell

a = 10.086 Å
b = 13.441 Å
c =  4.703 Å
β = 104.27°,  Z = 2

Identification

 

Color

pale green

Cleavage

Perfect on {010}

Mohs scale hardness

1.5 - 2

Diaphaneity

Transparent to translucent

Specific gravity

2.68 g/m3

Optical properties

Biaxial (+)

Refractive index

nα = 1.579 - 1.616
nβ = 1.602 - 1.656
nγ = 1.629 - 1.675

Birefringence

 δ = 0.050 - 0.059

Pleochroism

Visible;
X = blue, deep blue, indigo-blue
Y = pale yellowish green, pale bluish green, yellow-green
Z = pale yellowish green, olive-yellow

2V angle

Measured: 63° to 83.5°
Calculated: 78° to 88°

Dispersion

r<v, weak