Metavivianite

Metavivianite
A 6x4 cm specimen of paramorphosed olive-green to green Metavivianite after oxidized vivianite. From Kerchenskoe deposit, Crimea Oblast, Ukraine. Photo and collection specimen by Pavel Kartashov.
General
Category	Phosphate mineral
Formula (repeating unit)	Fe3+ 2(PO 4) 2(OH) 2·6H 2O
Strunz classification	8.DC.25 (10 ed) 7/C.14-20 (8 ed)
Dana classification	40.11.9.4
Crystal system	Triclinic
Crystal class	Pinacoidal (1)
Space group	P1
Unit cell	a = 7.989(1) Å, b = 9.321(2) Å c = 4.629(1) Å; α = 97.34(1)°; β = 95.96(1)°; γ = 108.59(2)°
Identification
Formula mass	443.734 g/mol
Color	Dark blue to blue-black; Dark green to green-black
Crystal habit	Bladed crystals, often with irregular acute multiple terminations.
Twinning	{110}
Cleavage	Perfect on {110}
Tenacity	Sectile
Mohs scale hardness	1.5-2
Luster	Sub-vitreous, Resinous, Greasy, Dull
Streak	Blue or greenish blue
Diaphaneity	translucent
Specific gravity	2.69
Optical properties	Biaxial (+)
Refractive index	nα = 1.600 - 3.000, nβ = 1.640 - 3.000, nγ = 1.685 - 3.000[1]
Birefringence	δ = 0.050 - 0.085
Pleochroism	Visible; X = blue to blue-green; Y,Z = yellow-green
2V angle	Measured: 85° (5), Calculated: 90°
Dispersion	Very weak
Ultraviolet fluorescence	Not fluorescent
References	[1][2][3]

Metavivianite (Fe³⁺
₂(PO
₄)
₂(OH)
₂·6H
₂O) is a hydrated iron phosphate mineral found in a number of geological environments. As a secondary mineral it is typically formed from oxidizing dehydrated vivianite.^[1] Metavivianite is typically found as dark blue or dark green prismatic to flattened crystals.

It was named by , Eric J. Essene, and in 1974 for its structural relationship to vivianite.^[2]

See also[]

• List of minerals

References[]