Fermiite

Fermiite is a rare uranium mineral with the formula Na₄(UO₂)(SO₄)₃·3H₂O.^[4] Chemically related minerals include oppenheimerite, meisserite (which is also structurally-related to fermiite),^[3] belakovskiite, natrozippeite and plášilite.^{[5][6][7][8][9]} Fermiite comes from the Blue Lizard mine, San Juan County, Utah, USA, which is known for many rare uranium minerals.^[2][3][10] The name honors Enrico Fermi (1901–1954).^[3]

Fermiite
General
Category	Sulfate mineral
Formula	Na4(UO2)(SO4)3·3H2O
IMA symbol	Fmi[1]
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) H-M symbol: (mm2)
Space group	Pmn21
Unit cell	a = 11.84, b = 7.87 c = 15.33 [Å] (approximated); Z = 4
Identification
Color	Pale greenish-yellow
Crystal habit	prismatic
Cleavage	None
Tenacity	Brittle
Mohs scale hardness	2.5
Streak	White
Diaphaneity	Transparent
Density	3.31 (calculated); 3.23 (measured)
Optical properties	Biaxal (+)
Refractive index	nα=1.52, nβ=1.53, nγ=1.57 (approximated)
Pleochroism	Colourless (X & Y), pale greenish-yellow (Z)
2V angle	50o (calculated)
Other characteristics	Radioactive
References	[2][3]

Association

Fermiite is closely associated with numerous other sulfate minerals: oppenheimerite, bluelizardite, wetherillite, blödite, manganoblödite, chalcanthite, epsomite, gypsum, hexahydrite, kröhnkite, sideronatrite and tamarugite.^[4]

Crystal structure

The main building block of the crystal structure of fermiite is a chain of the composition (UO₂)(SO₄)₃. Chains are connected with five types of Na-O polyhedra.^[4]