Changbaiit
| Changbaiit | |
|---|---|
| General and classification | |
| chemical formula | PbNb 2 O 6 |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.DF.10 ( 8th edition : IV / D.30) 03/08/11/01 |
| Crystallographic Data | |
| Crystal system | trigonal |
| Crystal class ; symbol | ditrigonal-pyramidal; 3 m |
| Space group | R 3 m (No. 160) |
| Lattice parameters | a = 10.50 Å ; c = 11.55 Å |
| Formula units | Z = 9 |
| Frequent crystal faces | {0001}, {000 1 }, {01 1 1}, {10 1 1 }, {10 1 2}, {01 1 2 }, {11 2 0} |
| Physical Properties | |
| Mohs hardness | 5.5 |
| Density (g / cm 3 ) | measured: 6.48; calculated: 6.51 |
| Cleavage | completely after {0001} |
| Break ; Tenacity | hooked, mussel-like; brittle |
| colour | colorless, creamy white, light brown, yellowish brown, yellowish green |
| Line color | White |
| transparency | transparent to translucent |
| shine | Diamond luster, pearlescent luster |
| Crystal optics | |
| Refractive indices |
n ω = 2.476 n ε = 2.485 |
| Birefringence | δ = 0.009 |
| Optical character | uniaxial positive |
Changbaiit is an extremely rare mineral from the mineral class of "oxides and hydroxides". It crystallizes in the trigonal crystal system with the chemical composition PbNb 2 O 6 , i.e. it consists of lead , niobium and oxygen in a molar ratio of 1: 2: 6 or, more generally, the ratio of metal: oxygen = 1: 2.
Changbaiit develops tabular crystals and spherulitic mineral aggregates up to about five millimeters in size with a diamond-like or pearl- like sheen on the surfaces, depending on the form . In its pure form, Changbaiit is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and, due to foreign admixtures, take on a light brown or yellowish brown to yellowish green color, the transparency decreasing accordingly. Its line color is white.
Etymology and history
Changbaiit was first discovered in an unnamed deposit in the Changbai Mountains near the city of Tonghua in the south of the Chinese province of Jilin ( Kirin ) and described in 1979 by Department 8 of the Geological Brigade Unit responsible for the Tonghua region and the Mineralogical and Petrological Laboratory of the Geological Institute Jilin Sciences.
The mineral was named after its type locality , the Changbai Mountains.
classification
Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the changbaiite belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with a molar ratio of metal: oxygen = 1: 2 (MO 2 and related compounds) “, Where he and Rosiait formed the unnamed group IV / D.30 .
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 assigns Changbaiit to the division of "Oxides with the molar ratio of metal: oxygen = 1: 2 and comparable". However, this is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral is classified in the sub-section “With large (± medium-sized) cations; dimer and trimer edge-sharing octahedra ”can be found, where it is the only member of the unnamed group 4.DF.10 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Changbaiit to the class of "oxides and hydroxides", but there in the category of "multiple oxides with Nb, Ta and Ti". Here he can be found again together with Rosiait in the unnamed group 08.03.11 within the sub-section “Multiple oxides with Nb, Ta and Ti and the formula A (B 2 O 6 )”.
Chemism
In its pure form, Changbaiit consists of 38% niobium, 42.4% lead and 19.6% oxygen in the form of Nb 2 O 5 and PbO.
Crystal structure
Changbaiit crystallizes trigonal in the space group R 3 m (space group no. 160) with the lattice parameters a = 10.50 Å and c = 11.55 Å as well as 9 formula units per unit cell .
Education and Locations
Changbaiit forms together with quartz and alkali feldspars in with kaolinite filled cores and cavities in alkali granites .
In addition to its type locality, the Changbai Mountains in the Chinese province of Jilin, the mineral is known so far (as of 2015) only from the Sierra Blanca Peaks in Hudspeth County in the US state of Texas.
See also
literature
- Detachment No. 8, Comprehensive Geological Brigade of Tonghua Region and the Laboratory of Petrology and Mineralogy Laboratory and Jilin Institute of Geological Science: Changbaiite (PbNb 2 O 6 ), a new mineral of lead and niobium from eastern Kirin, China. In: Acta Geologica Sinica Volume 52 (1), 1978, pp. 53-62 (Chinese with a brief description in English)
- Michael Fleischer, George Y. Chao, Adolf Pabst: New Mineral Names. In: American Mineralogist. Volume 64, 1979, pp. 241–245 ( PDF 509.8 kB )
Web links
Individual evidence
- ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 218 .
- ↑ a b Webmineral - Changbaiite
- ↑ a b c d Changbaiite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 70.1 kB )
- ↑ a b c Mindat - Changbaiite
- ↑ Find location list for Changbaiit at the Mineralienatlas and at Mindat