| Boltwoodite | |
|---|---|
 Acicular crystals of umber-yellow boltwoodite from Namibia (size: 1.8 × 1.7 × 1.4 cm) | |
| General | |
| Category | Uranium silicate mineral |
| Formula (repeating unit) | (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]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Mineralienatlas
- ^ Handbook of Mineralogy
- ^ Mindat.org
- ^ a b Webmineral data
- ^ Burns, Peter (1998). "The Structure of Boltwoodite and Implications of Solid Solution Toward Sodium Boltwoodite". The Canadian Mineralogist. 36: 1069-75.
- ^ Burns, Peter (1998). "The Structure of Boltwoodite and Implications of Solid Solution Toward Sodium Boltwoodite". The Canadian Mineralogist. 36: 1069-75.
- ^ "BOLTWOODITE (Hydrated Potassium Uranyl Silicate Hydroxide)".