Olmsteadite
| Olmsteadite | |
|---|---|
| General and classification | |
| other names |
IMA 1974-034 |
| chemical formula | KFe 2 (Nb, Ta) [O | PO 4 ] 2 · H 2 O |
|
Mineral class (and possibly department) |
Water-containing phosphates with foreign anions |
|
System no. to Strunz and to Dana |
8.DJ.05 ( 8th edition : VII / D.39) 07.22.11.01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-pyramidal mm 2 |
| Space group | Pb 2 1 m |
| Lattice parameters | a = 7.512 Å ; b = 10.00 Å; c = 6.492 Å Please complete the source as an individual reference |
| Formula units | Z = 1 Please complete the source as an individual reference |
| Physical Properties | |
| Mohs hardness | 4th |
| Density (g / cm 3 ) | 3.31 to 3.36 |
| Cleavage | good after {001} and {100} |
| colour | black, brown, red-brown |
| Line color | olive green |
| transparency | transparent to translucent |
| shine | Please complete |
| radioactivity | hardly noticeable |
| Crystal optics | |
| Refractive indices |
n α = 1.725 to 1.765 n β = 1.755 to 1.775 n γ = 1.815 to 1.835 |
| Birefringence | δ = 0.090 |
| Optical character | biaxial positive |
| Axis angle | 2V = 60 ° |
| Pleochroism | blue-yellow-yellow-brown |
Olmsteadite is a very rare mineral from the mineral class of water-containing phosphates with foreign anions. It crystallizes in the orthorhombic crystal system with the general chemical composition KFe 2 (Nb, Ta) [O | PO 4 ] 2 · H 2 O and usually develops small, long prismatic crystals of black, brown to red-brown color.
Niobium (Nb) and tantalum (Ta) are freely interchangeable , but always have the same molar ratio to the remaining components of the mineral.
Etymology and history
The mineral was in 1973 by Milo Olmstead in the type locality , the Big Chief Quarry in Glendale near Keystone ( South Dakota ) and WL Roberts at Custer found also in South Dakota. It was named after Olmstead.
classification
In the old (8th edition) and new systematics of minerals (9th edition) according to Strunz , the olmsteadite belongs in a group with johnwalkite to the department of "water-containing phosphates with foreign anions ". Since the new Strunz'schen mineral classification, this department is more precisely divided according to the size of the cations and the ratio of hydroxyl group to cation complex and the mineral is now in the subdivision “With large and medium-sized cations; (OH etc.): RO 4 = 1: 1 “, where it forms the unnamed group“ 8.DJ.05 ” together with Johnwalkite, Gatumbait , Camgasit , Phosphofibrite , Jungit , Wycheproofit , Ercitit , Attikait and Mrázekit .
The systematics used in the English-speaking world of minerals according to Dana assigns the olmsteadite to the division of " hydrated phosphates etc., with hydroxyl or halogen with (AB) 5 (XO 4 ) 3 Z q • x (H 2 O) ", where it than forms the Olmsteadit group with Johnwalkerite.
Education and Locations
Olmsteadite forms hydrothermally in phosphate springs, especially in pegmatites . It is accompanied by siderite and quartz .
In addition to the type locality, olmsteadite was found in two other mines near Keystone (South Carolina).
Crystal structure
Olmsteadite crystallizes in the orthorhombic crystal system in the space group Pb2 1 m with the lattice parameters a = 7.512 Å , b = 10.00 Å and c = 6.492 Å as well as one formula unit per unit cell .
See also
Individual evidence
literature
- Stefan Weiß: The large Lapis mineral directory . 4th edition. Christian Weise Verlag, Munich 2002, ISBN 3-921656-17-6 .
- Paul B. Moore, Takaharu Araki, Anthony R. Kampf, Ian M. Steele: Olmsteadite, K 2 Fe 2+ 2 [Fe 2+ 2 (Nb, Ta) 5+ 2 O 4 (H 2 O) 4 (PO 4 ) 4 ], a new species, its crystal structure and relation to vauxite and montgomeryite. In: American Mineralogist. 1976, 61, pp. 5-11 ( pdf ).