Günterblassit
| Günterblassit | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (K, Ca) 3 Fe [(Si, Al) 13 O 25 (OH, O) 4 ] ⋅7H 2 O |
|
Mineral class (and possibly department) |
Silicates and germanates - layered silicates |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-pyramidal; mm 2 |
| Space group | Pnm 2 1 (No. 31, position 2) |
| Lattice parameters | a = 6.538 Å ; b = 6.970 Å; c = 37.216 Å |
| Formula units | Z = 2 |
| Frequent crystal faces | {001}, {010}, {100} |
| Twinning | - |
| Physical Properties | |
| Mohs hardness | 4th |
| Density (g / cm 3 ) | measured: 2.18; calculated: 2.17 |
| Cleavage | Perfect |
| colour | colorless, occasionally white, pale yellow to brown |
| Line color | White |
| transparency | clear as water |
| shine | not specified |
| Crystal optics | |
| Refractive indices |
n α = 1.488 n β = 1.490 n γ = 1.493 |
| Birefringence | δ = 0.005 |
| Optical character | biaxial positive |
| Axis angle | 2V = 80 ° |
| Pleochroism | - |
The mineral Günterblassite is a very rarely occurring sheet silicate from the Günterblassite group with the idealized chemical composition (K, Ca) 3 Fe [(Si, Al) 13 O 25 (OH, O) 4 ] ⋅7H 2 O. It crystallizes in the orthorhombic crystal system and develops colorless, rectangular, platy to tabular crystals a few millimeters in size.
Günterblassite forms late magmatically in miaroles of alkali basalts and occurs there together with nepheline , leucite , augite , phlogopite , Åkermanite , magnetite , perovskite , idolite and fluorapatite . Except in its type locality , the basalt quarry "Rother Kopf" near Gerolstein in the Vulkaneifel , Rhineland-Palatinate , Germany, Günterblassite has so far only been found in the basalt quarry "Graulay" near Hillesheim , also in the Vulkaneifel.
Etymology and history
Günterblassit was discovered in 2012 by a group of Russian mineralogists in a sample that was collected in 2010 in the "Rother Kopf" quarry near Gerolstein in the Vulkaneifel. Günterblassit was the first layered silicate with a 3-layer structure and was named after the German amateur mineralogist Günter Blass , in recognition of his extensive work on the minerals of the Eifel. Günter Blass was involved in the first description of numerous minerals, including pattersonite , allanpringite , schäferite , lukrahnite , hechtsbergite , ferriallanite (La) , Windhoekite and perrierite (La) . Since then, two more sheet silicates with the same 3-layer structure have been discovered: Umbrianite (2011) and Hillesheimite (2012).
classification
Günterblassit is a new type of 3-layer silicate, for which the current systematics according to Strunz or Dana do not yet contain a group.
Chemism
The composition measured from the type locality is [10] (□ 0.4 K 0.35 Ca 0.25 ) [8] (K 0.85 □ 0.6 Ba 0.3 Ca 0.25 ) [7] (Fe 2+ 0.5 Ca 0.2 Mg 0.15 Na 0.15 ) [ [4] (Si 9.91 Al 3.09 ) O 25.25 (OH) 3.75 ] ⋅7.29H 2 O, where the coordination number of the positions in the crystal structure are given in square brackets .
The composition is quite variable. Iron (Fe 2+ ) can be replaced by magnesium (Mg 2+ ), potassium (K + ) in part by calcium (Ca 2+ ) and barium (Ba 2+ ) or vacancies. The deviations of the Si-Al ratio from the ideal value of 10: 3 observed so far are small. The OH contents vary between 3 and 4 OH per formula unit.
Crystal structure
Günterblassite crystallizes with orthorhombic symmetry of the space group Pnm 2 1 (space group no. 31, position 2) and the lattice parameters a = 6.538 Å , b = 6.975 Å and c = 37.26 Å as well as two formula units per unit cell .
Aluminum and silicon are surrounded by 4 oxygen in such a way that the cation lies in the center of a tetrahedron, the corners of which are formed by the oxygen ions. These coordination tetrahedra are linked by their corners to form rings of four. These rings are connected to each other in layers, with new rings made up of 8 tetrahedra.
Günterblassit has these layer units of 4 and 8 rings in common z. B. with the minerals of the Mountainite family (single layers) and Rhodenite family (double layers). Structurally closely related are the minerals of the Delhayelite family, which also have aluminosilicate layers made up of rings of 4 and 8.
In Günterblassit, three of these layers are linked by tetrahedron tips to form three-layer packages, with the middle layer being supplemented by a further aluminosilicate tetrahedron. Between the three layers, zeolite-like channels made of rings of 8 run through the layer packages along the a and b axes.
Water (H 2 O) and potassium (K + ) are built into these channels . There the potassium is surrounded by 8 oxygen.
The layers of layers are interconnected by iron (Fe 2+ , subordinate to Mg 2+ , Ca 2+ , Na + ) and potassium. The Fe position is surrounded by 7 oxygen and the potassium position is surrounded by 10 oxygen.
Education and Locations
Günterblassite forms late magmatically in miaroles of alkali basalts . It is assumed that Günterblassit in the reaction of a structurally related tectosilicate such. B. Leucite is formed with aqueous solutions.
In its type locality , the basalt quarry "Rother Kopf" near Gerolstein in the Vulkaneifel , Rhineland-Palatinate, Germany, Günterblassite occurs together with nepheline , leucite , augite , phlogopite , Åkermanite , magnetite , perovskite , idolite and fluorapatite . The only other documented site to date is the Graulay basalt quarry near Hillesheim , also in the Eifel. This is also the type locality of Hillesheimite , another 3-layer silicate from the Günterblassite group discovered in 2012.
See also
Web links
Individual evidence
- ↑ a b c d e f Ramiza K. Rastsvetaeva, Sergey M. Aksenov, Nikita V. Chukanov: Crystal Structure of Günterblassite, a New Mineral with a Triple Tetrahedral Layer . In: Doklady Chemistry . tape 442 , no. 2 , February 2012, p. 57-62 , doi : 10.1134 / S0012500812020115 ( full text ).
- ↑ a b c d e f g h i j k l m n o p q Nikita V. Chukanov, Ramiza K. Rastsvetaeva, Sergey M. Aksenov, Igor V. Pekov, Natalia V. Zubkova, Sergey N. Britvin, Dmitriy I Belakovskiy, Willy Schüller, Bernd Ternes: Günterblassite, (K, Ca) 3-x Fe [(Si, Al) 13 O 25 (OH, O) 4 ] ⋅7 H 2 O, a New Mineral: the First Phyllosilicate with Triple Tetrahedral Layer . In: Geology of Ore Deposits . tape 54 , no. 8 , 2012, p. 656-662 , doi : 10.1134 / S1075701513070064 ( full text ).
- ↑ a b Graulay (Graulai; Graulei; Grauley), Hillesheim, Eifel, Rhineland-Palatinate, Germany