Chemistry:Dessauite-(Y)
| Dessauite-(Y) | |
|---|---|
| General | |
| Category | Oxide mineral Crichtonite group |
| Formula (repeating unit) | (Sr,Pb)(Y,U)(Ti,Fe3+)20O38 |
| Strunz classification | 4.CC.40 |
| Crystal system | Trigonal |
| Crystal class | Rhombohedral (3) H-M symbol: (3) |
| Space group | R3 |
| Unit cell | a = 9.197 Å, α = 68.75° |
| Identification | |
| Formula mass | 1,856.57 g/mol |
| Color | Black; ash-grey with pale bluish tones. |
| Crystal habit | Tabular |
| Cleavage | None |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6 1⁄2 – 7 |
| |re|er}} | Metallic luster |
| Streak | Black |
| Diaphaneity | Opaque |
| Density | 4.68 g/cm3 (calculated) |
| Birefringence | Low |
| Pleochroism | Very weak |
Dessauite-(Y) is a mineral member of the crichtonite group with the formula (Sr,Pb)(Y,U)(Ti,Fe3+)20O38. It is associated with derbylite, hematite, rutile, karelianite, siderite, and calcite. Founded in the Buca della Vena Mine, Tuscany, Italy, the mineral was called dessauite in honor of professor Gabor Dessau (1907–1983).[2]
Structure
Dessauite occurs as small, flattened rhombohedral crystals, tabular {001} with hexagonal outline. Members of the crichtonite group may be confused with ilmenite or hematite.[3] The difference between dessauite and other minerals in the crichonite group is the occurrence of three additional octahedral sites and of a site in square pyramidal coordination, all with low occupancies. The mineral is black and opaque, presents a metallic luster, and it is brittle. Dessauite presents dimensions of diameter up to 1mm and thickness up to 0.2 mm. In reflected plane-polarized light the color is ash-grey with pale bluish tones.[2] The calculated density is 4.68 g/cm3. The habit is tabular, forming thin dimensions in one direction and hardness of 6.5 and 7.[4] Dessauite differs from other elements of the crichtonite group because of the quantity of cations and X-ray diffraction pattern.
Occurrence
Dessauite was found in the Buca della Vena Mine, Apuan Alps, northern Tuscany, Italy, with many other minerals, coming from hydrothermal fluids circulating through a small hematite-barite ore deposit within dolomite, during an alpine metamorphic event. It occurs in calcite veins hosted within dolomite and is associated with calcite, rutile, hematite, siderite, and derbylite.[2]
See also
References
- ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
- ↑ 2.0 2.1 2.2 Orlandi, Paolo (1997). "Dessauite, (Sr,Pb)(Y,U)(Ti,Fe3+)20O38, a new mineral of the crichtonite group from Buca della Vena mine, Tuscany, Italy.". Journal of the Mineralogical Society of America. http://www.minsocam.org/msa/ammin/toc/Articles_Free/1997/Orlandi_p807-811_97.pdf.
- ↑ "Crichtonite Group". http://www.mindat.org/min-29190.html.
- ↑ "Dessauite Mineral Data". http://www.webmineral.com/data/Dessauite.shtml#.Vl8dlnarTIU.
 |  |
