Boltwoodite
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CategoryUranium silicate mineral
Formula(K0.56Na0.42)[(UO2)(SiO3OH)]·1.5(H2O)
Strunz classification9.AK.15
| Boltwoodite | |
|---|---|
 Acicular crystals of umber-yellow boltwoodite from Namibia (size: 1.8 × 1.7 × 1.4 cm) | |
| General | |
| Category | Uranium silicate mineral |
| Formula | (K0.56Na0.42)[(UO2)(SiO3OH)]·1.5(H2O) |
| IMA symbol | Bdw[1] |
| Strunz classification | 9.AK.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/m |
| Unit cell | a = 7.0772(8) Å, b = 7.0597(8) Å, c = 6.6479(7) Å; β = 104.982(2)°; Z = 2 |
| Identification | |
| Color | Pale yellow, orange yellow |
| Crystal habit | Elongated crystals, acicular to fibrous |
| Cleavage | Perfect on {010}, imperfect on {001} |
| Tenacity | Brittle |
| Mohs scale hardness | 3.5–4 |
| Luster | Silky to vitreous, dull or earthy in aggregates |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 4.7 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.668 – 1.670 nβ = 1.695 – 1.696 nγ = 1.698 – 1.703 |
| Birefringence | δ = 0.030 – 0.033 |
| Pleochroism | Weak, X = colorless, Y = Z = yellow |
| Ultraviolet fluorescence | Fluoresces dull green in both SW and LW UV |
| Other characteristics |  Radioactive |
| References | [2][3][4][5][6] |
Boltwoodite is a hydrated uranyl silicate mineral with formula (K0.56Na0.42)[(UO2)(SiO3OH)]·1.5(H2O), distinct in crystal structure from sodium boltwoodite, which has an orthorhombic structure rather than monoclinic.[7] It is formed from the oxidation and alteration of primary uranium ores. It takes the form of a crust on some sandstones that bear uranium. These crusts tend to be yellowish with a silky or vitreous luster.[5][8]
