Boltwoodite

The mineral Boltwoodite is a rarely occurring uranium mineral with the chemical composition ( K0.56Na0.44 ) [( UO2) ( SiO3OH )] • 1.5 H2O. It crystallizes in the monoclinic crystal system and usually develops tufted, radial- yellow aggregates.

Special Features

The mineral is classified as highly radioactive due to its uranium content of up to about 55 % and has a specific activity of more than 99.3 kBq / g (compared to natural potassium 31 Bq / g).

Etymology and history

Boltwoodite was named in honor of Bertram Borden Boltwood radio chemist who developed the uranium - lead dating. The mineral was first described in 1956. 1981 succeeded Stohl and Smith, the crystal structure determination of twinned crystals in the formula ( H3O ) K [( UO2) (SiO4 )] ( H2O ) resulted. The work of other researchers, however, suggest that the potassium ions can also be replaced by sodium ions. In 1998, Burns managed a more accurate single-crystal structure, which determined the structural formula of the Boltwoodits as ( K0.56Na0.44 ) [( UO2) ( SiO3OH )] • 1.5 H2O. The structure of the SiO3OH group is further confirmed by infrared spectroscopy.

The type of mineral is located in the National Museum of Natural History in Washington, DC

Classification

The dated 8th edition of Strunz lists the Boltwoodite in the " Uranophangruppe " with the system no. VIII/B.34 and the other members cuprosklodowskite, Kasolit, Natroboltwoodit, Oursinit, Sklodowskit, uranophane and uranophane - beta.

The 9th, completely revised edition of Strunz lists the Boltwoodite in the Department K " uranyl island and layer silicates with a uranium: silicon ratio of U: Si = 2: 1" in the group 9.AK.15. This group includes further Kasolit, Natroboltwoodit, uranophane and uranophane - beta.

The commonly used in English-speaking classification of minerals according to Dana assigns the Boltwoodite in the Uranophangruppe the Department of island silicates, there, however, in the department of " island silicates with SiO4 groups and other anions and complex cations with ( UO2) " with the system no. 53.03.01.05 one.

Education and Locations

Boltwoodite found in the transformation zone of hydrated uranyl oxides associated with uraninite. It forms in pegmatitic rocks as well as in sandstone. Sites include the Delta mine in Utah ( USA) ( type locality ), the Green Monster Mine in Nevada ( USA) and in particular the Rössing mine in Namibia.

Crystal structure

Boltwoodite crystallizes in the monoclinic space group P 21 with the lattice parameters a = 7.077 Å; b = 7.060 Å; c = 6.650 Å with β = 104.98 ° and two formula units per unit cell. The basic structure of Boltwoodits consists of a chain-like layers of edge-sharing pentagonal bipyramidal Uranyleinheiten whose equatorial oxygen atoms are each connected by tetrahedrally coordinated silicon atoms. The silicon atoms coordinate between three Uranyleinheiten; the fourth binding site is saturated by a hydroxide ion. The K -, respectively, Na ions bridge the opposite uranyl units and coordinate the hydroxyl group of the silicon. The SiO3OH geometry corresponds to the structures of other minerals of the Uranophangruppe cuprosklodowskite, Sklodowskit, uranophane and uranophane - beta.

Precautions

When dealing with Boltwoodite is to ensure adequate radiation protection. To prevent incorporation ( uptake into the body ), is thorough hand washing after handling with bare hands is recommended.