Boltwoodite is a hydrated

uranyl The uranyl ion with the chemical formula has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen, with uranium in the oxidation state +6. Four or more ligands may be bound to the u ...

silicate mineral Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

with formula (K_0.56Na_0.42) UO₂)(SiO₃OH)�1.5(H₂O), distinct in crystal structure from sodium boltwoodite, which has an orthorhombic structure rather than monoclinic. It is formed from the

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

and alteration of primary

uranium Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...

ores. It takes the form of a crust on some

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s that bear uranium. These crusts tend to be yellowish with a silky or vitreous luster.

Discovery and occurrence

It was first described in 1956 for an occurrence in Pick's Delta Mine, Delta, San Rafael District (

San Rafael Swell The San Rafael Swell is a large geologic feature located in south-central Utah, United States about west of Green River. Measuring approximately , the swell consists of a giant dome-shaped anticline of sandstone, shale, and limestone that wa ...

Emery County, Utah Emery County is a County (United States), county in east-central Utah, United States. As of the 2020 United States census, the population was 9,825. Its county seat is Castle Dale, Utah, Castle Dale, and the largest city is Huntington, Utah, Hu ...

, US. It is named after Bertram Boltwood (1870–1927) an American pioneer of

radiochemistry Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads t ...

. Boltwoodite occurs as secondary silicate alteration crusts surrounding

uraninite Uraninite, also known as pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium c ...

and as fracture fillings. It is found in

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

s and sandstone uranium deposits of the

Colorado Plateau The Colorado Plateau is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the Southwestern United States. This plateau covers an area of 336,700 km2 (130,000 mi2) within w ...

-type. It occurs associated with uraninite,

becquerelite Becquerelite is a uranium mineral with the chemical formula: Ca(UO2)6O4(OH)6·8(H2O). It is a secondary mineral which contains calcium and is a bright yellow colour. It has a Mohs hardness of about 2. It was named after the French physicist Anto ...

fourmarierite Fourmarierite is a secondary uranium-lead mineral. It was named for the Belgian geologist Paul Fourmarier (1877–1970). Its chemical formula is . References Lead minerals Uranium(VI) minerals Orthorhombic minerals Minerals in space group ...

, phosphouranylite,

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

and

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scal ...

References

Uranium(VI) minerals Monoclinic minerals Minerals in space group 11 {{silicate-mineral-stub