Nováčekit
| Nováčekit | |
|---|---|
 Size: 2.1 × 2.0 × 0.4 cm. |
|
| General and classification | |
| other names |
Nováčekit-I |
| chemical formula | Mg (UO 2 ) 2 (AsO 4 ) 2 • 10-12H 2 O |
|
Mineral class (and possibly department) |
Phosphates, arsenates and vanadates |
|
System no. to Strunz and to Dana |
8.EB.05 ( 8th edition : VII / E.01) 40.02a.11.01 |
| Crystallographic Data | |
| Crystal system | triclinic (dodecahydrate) monoclinic (decahydrate) |
| Crystal class ; symbol | triclinic pinacoidal 1 or monoclinic prismatic 2 / m |
| Room group (no.) | P 1 or P 2 1 / c (No. 2 or 14) |
| Lattice parameters | see crystal structure |
| Formula units | see crystal structure |
| Physical Properties | |
| Mohs hardness | 2.5 |
| Density (g / cm 3 ) | 3.25 to 3.7 |
| Cleavage | completely after {001} |
| colour | straw yellow to lemon yellow |
| Line color | yellow white |
| transparency | translucent |
| shine | Wax gloss |
| radioactivity | weakly alpha emitting |
| Crystal optics | |
| Refractive indices | n α = 1.548 to 1.578 |
| Birefringence | δ = 0.03 |
| Optical character | uniaxial negative |
| Axis angle | 2V = 0 to 40 ° |
| Pleochroism | colorless, pale yellow |
Nováčekit is a collective name for the two independent minerals Nováčekit-I and Nováčekit-II (see also structure ). They belong to the autunit group within the mineral class of " phosphates , arsenates and vanadates ".
- Nováčekit-I crystallizes in the triclinic crystal system with the chemical composition Mg [UO 2 AsO 4 ] 2 • 12H 2 O
- Nováčekit-II in the monoclinic crystal system with the chemical composition Mg [UO 2 AsO 4 ] 2 • 10H 2 O.
The crystals are mostly flat and tabular and their shape is dominated by the base surface {001}. Lamellar and subparallel aggregates of platy crystals are common. Nováčekit is straw yellow to lemon yellow, transparent with a wax sheen. The stroke color is yellow-white. The density is 3.25 - 3.7 g / cm 3 and the Mohs hardness is between 2 and 3.
Etymology and history
Nováčekit was discovered in 1951 by Clifford Frondel while investigating secondary uranium minerals from the "Weißer Hirsch" pit near Schneeberg in Saxony , which had previously been mistaken for uranium spinite . He named the new mineral after the Czech mineralogist Radim Nováček in recognition of his contributions to the mineralogy of uranium.
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the Nováčekit belonged to the department of "Uranylphosphate / Arsenate and Uranylvanadate", where it together with Autunit , Fritzscheit , Heinrichit , Kahlerit , Torbernit , Trögerit , Sabugalit , Saléeit , Uranocircit , Uranospinit and Zeunerit the "Autunit Group" with the system no. VII / E.01 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies the Nováčekit in the "Uranyl phosphates and arsenates" section. However, this is further subdivided according to the ratio of uranium oxide complex (UO 2 ) to phosphate, arsenate or vanadate complex (RO 4 ), so that the mineral according to its composition in the subdivision "UO 2 : RO 4 = 1: 1" can be found where together with Autunit, Heinrichit, Kahlerit, Kirchheimerit, Saléeit, Torbernit, Uranocircit-I, Uranocircit-II, Uranospinit, Xiangjiangit, Zeunerit the "Autunit-Group" with the system no. 8.EB.05 forms.
The systematics of minerals according to Dana , which is predominantly used in the English-speaking world , also classifies the Nováčekit in the section of "water-containing phosphates etc.". Here it is together with Metanovácekit in the unnamed group 40.02a.10 within the subdivision of “Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O), with (UO 2 ) 2+ ”.
Crystal structure
| Crystallographic Data | Nováčekit I | Nováčekit II |
|---|---|---|
| Crystal system | triclinic | monoclinic |
| Space group | P 1 | P 2 1 / c |
|
Lattice parameters |
a = 7.1594 Å b = 7.1610 Å c = 11.3146 Å α = 81.391 ° β = 81.177 ° γ = 88.884 ° |
a = 7.1328 Å b = 20.085 Å c = 7.1569 Å β = 90.585 ° |
| Number (Z) of the formula units | Z = 1 | Z = 2 |
The structure is characterized by uranyl phosphate layers that are parallel to the (001) plane. Arsenic 5+ is tetrahedral surrounded by 4 oxygen atoms, the U 6+ octahedral by 6 oxygen atoms. The AsO 4 tetrahedra are linked with UO 6 octahedra over all 4 corners , the UO 6 octahedra over 4 corners with PO 4 tetrahedra.
The water molecules and the Mg ions are located between the uranyl arsenate layers. Every Mg 2+ is octahedrally coordinated by 6 water molecules. The remaining 4 - 6 water molecules are not directly bound to any cation. However, with a complex system of hydrogen bonds, they contribute to a balanced distribution of the charges and thus to the stabilization of the structure.
Nováčekit shows a tetragonal pseudo-symmetry, which results from the structure of the uranyarsenate layer. The distribution of the divalent cations and water molecules between these layers lower the symmetry. Nováčekit II with 10 H 2 O crystallizes monoclinically in the space group P2 1 / c and Nováčekit I with 12 H 2 O triclinic in the space group P-1.
properties
Due to its uranium content of up to 45%, Nováčekit is classified as very highly radioactive and has a specific activity of around 80.5 k Bq / g (for comparison: natural potassium 31.2 Bq / g).
Under ultraviolet light, Nováčekit shows a dull green to strong lemon yellow fluorescence .
As with the structurally related minerals saléeit , torbernite and zeunerite , the water content fluctuates between 12 H 2 0 (Nováčekit I) and 10 H 2 0 (Nováčekit II), which is easily converted into the less water-poor mineral Metanováčekit with 8 H 2 0.
morphology
Nováčekit forms rectangular to square crystals with tabular to leafy habit.
Education and Locations
Nováčekit is secondary to the weathering of uranium minerals in the oxidation zone of uranium-containing hydrothermal and sedimentary deposits.
In the uranium deposit near Schneeberg in Saxony , Nováčekit is associated with uranophane and zeunerite .
Numerous other occurrences are documented. In the Cherkasar deposit in Uzbekistan , nováčekite occurs together with schoepite , paraschoepite , arsenuranylite , metazeunerite and uranospinite . In Wheal Owles , England , nováčekite is found associated with chalcopyrite , arsenopyrite and sphalerite .
Precautions
Due to the toxicity and the high level of radioactivity of the mineral, mineral samples from the Nováčekit 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
Individual evidence
- ↑ a b c d e A. Locock, PC Burns, TM Flynn. (2004).
- ↑ a b Handbook of Mineralogy.
- ↑ C. Frondel (1951).
- ↑ Webmineral - Novacekite (English).
literature
- A. Locock, PC Burns, TM Flynn. (2004). Divalent Transition Metals And Magnesium in Structures That Contain the Autunite-Type Sheet Canadian Mineralogist: 42: pp. 1699-1718. ( PDF 2.38 MB )
- C. Frondel (1951): Studies on uranium minerals (IX): Saleeite and Novacekite , Am. Min. 36, pp. 525-530 ( PDF 473 kB )
- Anthony, JW, Bideaux, RA, Bladh, KW, and Nichols, MC (2000): Nováčekite , In: Handbook of Mineralogy, American Mineralogical Society ( PDF (68 kB) )
Web links
- Mineral Atlas: Novácekit I and Mineralienatlas: Novácekit II (Wiki)
- mindat.org : Mineral database