| Dessauite-(Y) | |
| Category: | Oxide mineral Crichtonite group |
| Imasymbol: | Dss-Y[1] |
| Molweight: | 1,856.57 g/mol |
| Strunz: | 4.CC.40 |
| System: | Trigonal |
| Class: | Rhombohedral H-M symbol: |
| Symmetry: | R |
| Unit Cell: | a = 9.197 Å, α = 68.75° |
| Color: | Black; ash-grey with pale bluish tones. |
| Habit: | Tabular |
| Cleavage: | None |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Mohs: | – 7 |
| Luster: | Metallic luster |
| Birefringence: | Low |
| Pleochroism: | Very weak |
| Streak: | Black |
| Density: | (calculated) |
| Diaphaneity: | Opaque |
Dessauite-(Y) is a mineral member of the crichtonite group with the formula . 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]
Dessauite occurs as small, flattened rhombohedral crystals, tabular 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 0.2mm. In reflected plane-polarized light the color is ash-grey with pale bluish tones. 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.
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.