Boltwoodite
| Boltwoodite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (K 0.56 Na 0.44 ) [(UO 2 ) (SiO 3 OH)] • 1.5 H 2 O |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.AK.15 ( 8th edition : VIII / B.34) 53.03.01.05 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic sphenoid; 2 |
| Space group | P 2 1 (No. 4) |
| Lattice parameters |
a = 7.0772 Å ; b = 7.0597 Å; c = 6.6479 Å β = 104.98 ° |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | 3.5 to 4 |
| Density (g / cm 3 ) | 4.6 |
| Cleavage | completely after {010}, clearly after {001} |
| Break ; Tenacity | uneven |
| colour | yellow, light yellow |
| Line color | White |
| transparency | translucent |
| shine | Glass gloss, mother-of-pearl gloss, wax gloss |
| radioactivity | very strong |
| Crystal optics | |
| Refractive indices |
n α = 1.668 to 1.670 n β = 1.695 to 1.696 n γ = 1.698 to 1.703 |
| Birefringence | δ = 0.030 to 0.033 |
| Optical character | biaxial negative |
| Pleochroism | weak: X = colorless, Y = Z = yellow |
The mineral boltwoodite is a rather seldom occurring uranium mineral with the chemical composition (K 0.56 Na 0.44 ) [(UO 2 ) (SiO 3 OH)] · 1.5 H 2 O. It crystallizes in the monoclinic crystal system and develops mostly tufted, radial yellow Aggregates.
Etymology and history
Boltwoodite was named in honor of radio chemist Bertram Borden Boltwood , who developed uranium-lead dating . The mineral was first described in 1956. In 1981, Stohl and Smith succeeded in determining the structure of twinned crystals, which resulted in the formula (H 3 O) K [(UO 2 ) (SiO 4 )] (H 2 O). However, the work of other scientists suggests that the potassium ions can also be replaced by sodium ions. In 1998 Burns finally succeeded in a more precise single-crystal structure analysis which determined the structural formula of boltwoodite as (K 0.56 Na 0.44 ) [(UO 2 ) (SiO 3 OH)] • 1.5 H 2 O. The structure of the SiO 3 OH group is also substantiated by infrared spectroscopy .
The type mineral is located in the National Museum of Natural History in Washington, DC under catalog number 112710
classification
The outdated 8th edition of the Strunz lists the boltwoodite in the "Uranophangruppe" with the system no. VIII / B.34 and the other members Cuprosklodowskit , Kasolit , Natroboltwoodit , Oursinit , Sklodowskit , Uranophan and Uranophan-beta .
The 9th, completely revised edition of Strunz lists the boltwoodite in the section K " Uranyl island and polysilicates with a uranium: silicon ratio of U: Si = 2: 1 " in group 9.AK.15 . This group also includes Kasolit, Natroboltwoodit, Uranophan and Uranophan-beta.
The systematics of minerals according to Dana , which is common in the English-speaking world , assigns boltwoodite to the uranophane group of the island silicates department, but there in the department of " island silicates with SiO 4 groups and other anions as well as complex cations with (UO 2 ) " with the system No. 53.03.01.05 a.
Crystal structure
Boltwoodite crystallizes monoclinically in the space group P 2 1 (space group no. 4) with the lattice parameters a = 7.0772 Å ; b = 7.0597 Å; c = 6.6479 Å with β = 104.98 ° and 2 formula units per unit cell .
The basic structure of boltwoodite consists of layers of chain-shaped, edge-linked pentagonal-bipyramidal uranyl units , the equatorial oxygen atoms of which are each connected by tetrahedrally coordinated silicon atoms . The silicon atoms coordinate three uranyl units; the fourth binding site is saturated by a hydroxide ion . The K + and Na + ions bridge the opposite uranyl units and coordinate the hydroxyl group of silicon. The SiO 3 OH geometry corresponds to the structures of the other minerals of the uranophane group cuprosklodovskite, sklodovskite, uranophane and uranophane-beta.
properties
The mineral is classified as highly radioactive due to its uranium content of up to 55% and has a specific activity of more than 99.3 k Bq / g (for comparison: natural potassium 31 Bq / g).
Education and Locations
Boltwoodite is found in the transformation zone of hydrated uranyl oxides, associated with uraninite . It forms in pegmatitic rock 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.
Precautions
Due to the toxicity and the strong radioactivity of the mineral, mineral samples from boltwoodite should only be kept in dust-tight and radiation-proof containers, but especially never in living rooms, bedrooms or work rooms. Absorption into the body (incorporation, ingestion ) should also be prevented in any case and, for safety, direct body contact should be avoided and respiratory protection mask and gloves should be worn when handling the mineral .
See also
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 .
- Boltwoodite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 81.2 kB )
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 .
Web links
Individual evidence
- ↑ a b c d e RC Burns: The Structure of Boltwoodite and Implications of Solid Solution Toward Sodium Boltwoodite , American Mineralogist Volume 36, 1998, pp. 1069-1075 ( PDF 582 kB )
- ↑ a b Webmineral - Boltwoodite
- ↑ a b Boltwoodite at mindat.org