Belakovskiite

Belakovskiite is a very rare uranium mineral with the formula Na₇(UO₂)(SO₄)₄(SO₃OH)(H₂O)₃.^[2][3] It is interesting in being a natural uranyl salt with hydrosulfate anion, a feature shared with meisserite.^[5] Other chemically related minerals include fermiite, oppenheimerite, natrozippeite and plášilite.^[6][7][8][9] Most of these uranyl sulfate minerals was originally found in the Blue Lizard mine, San Juan County, Utah, US.^[10] The mineral is named after Russian mineralogist Dmitry Ilych Belakovskiy.^[2]

Belakovskiite
General
Category	Sulfate mineral
Formula	Na7(UO2)(SO4)4(SO3OH)(H2O)3
IMA symbol	Bkk[1]
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 5.46, b = 11.33, c = 18.42 [Å], α = 104.77°, β = 90.09°, γ = 96.77° (approximated); Z = 2
Identification
Color	Yellow-green
Crystal habit	fibrous
Cleavage	None
Tenacity	Brittle
Mohs scale hardness	2
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Density	3.31 (calculated); 3.23 (measured)
Optical properties	Biaxal (+)
Refractive index	nα=1.50, nβ=1.51, nγ=1.52 (approximated)
Pleochroism	None
2V angle	88o (calculated)
Other characteristics	Radioactive
References	[2][3][4]

Association

Belakovskiite is associated with other sulfate minerals: meisserite, blödite, ferrinatrite, kröhnkite, and metavoltine.^[2] This association is found as efflorescences on a sandstone associated with uranium mineralization.^[4]

Crystal structure

The framework of belakovskiite crystal structure is a hexavalent cluster with composition (UO₂)(SO₄)₄(H₂O). Such clusters are connected via Na-O and hydrogen bonds.^[2]