Dessauite-(Y)
| Dessauite-(Y) | |
|---|---|
| General | |
| Category | Oxide mineral Crichtonite group |
| Formula (repeating unit) |
(Sr,Pb)(Y,U)(Ti,Fe3+)20O38 |
| Unit cell | a = 9.197 Å, α = 68.75° |
| Identification | |
| Formula mass | 1,856.57 gm |
| Color | Black; ash-grey with pale bluish tones. |
| Crystal habit | Tabular |
| Crystal system | Trigonal |
| Cleavage | None |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6½ - 7 |
| Luster | 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).[1]
Contents
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.[2] 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 0.2mm. In reflected plane-polarized light the color is ash-grey with pale bluish tones.[1] 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.[3] Dessauite differs from other elements of the crichtonite group because of the quantity of cations and X-ray diffraction patter.
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.[1]
