Boltwoodite

Boltwoodite
Acicular crystals of umber-yellow boltwoodite from Namibia (size: 1.8 × 1.7 × 1.4 cm)
General
CategoryUranium silicate mineral
Formula
(repeating unit)
(K0.56Na0.42)[(UO2)(SiO3OH)]·1.5(H2O)
IMA symbolBdw[1]
Strunz classification9.AK.15
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/m
Unit cella = 7.0772(8) Å,
b = 7.0597(8) Å,
c = 6.6479(7) Å;
β = 104.982(2)°; Z = 2
Identification
ColorPale yellow, orange yellow
Crystal habitElongated crystals, acicular to fibrous
CleavagePerfect on {010}, imperfect on {001}
TenacityBrittle
Mohs scale hardness3.5–4
LusterSilky to vitreous, dull or earthy in aggregates
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity4.7
Optical propertiesBiaxial (−)
Refractive indexnα = 1.668 – 1.670 nβ = 1.695 – 1.696 nγ = 1.698 – 1.703
Birefringenceδ = 0.030 – 0.033
PleochroismWeak, X = colorless, Y = Z = yellow
Ultraviolet fluorescenceFluoresces 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]

  1. ^ 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.
  2. ^ Mineralienatlas
  3. ^ Handbook of Mineralogy
  4. ^ Mindat.org
  5. ^ a b Webmineral data
  6. ^ Burns, Peter (1998). "The Structure of Boltwoodite and Implications of Solid Solution Toward Sodium Boltwoodite". The Canadian Mineralogist. 36: 1069-75.
  7. ^ Burns, Peter (1998). "The Structure of Boltwoodite and Implications of Solid Solution Toward Sodium Boltwoodite". The Canadian Mineralogist. 36: 1069-75.
  8. ^ "BOLTWOODITE (Hydrated Potassium Uranyl Silicate Hydroxide)".